feat(ai): 写作模式拆成自由创作与模板两条路（issue 18）

自由创作不再解析自然语言：原话整段作为 userContent 下发，docType 留空，由后端转
「AI 创意助手」。选了文体才提交 docType 等结构化条件，走「内容创作与宣传助手」。

- writing-params.ts 删掉 parseWritingRequest、字段别名表与字数兜底表，只留选项常量。
- chatgpt/index.vue：字数选择器只在选中文体后出现；撤掉图片比例选择器（上游开始
  节点无比例变量，只能拼进 user_content，等于替上游写 prompt）；结果不再用入参补标题。
- gxmu/manuscriptGen：新增「自由创作」入口与 freeContent 文本域，模板模式才展开活动
  信息等可选项。
- 顺带删除 chatgpt/index.bak.vue 旧备份。

src/views/oa/chatgpt/index.vue

@@ -226,32 +226,20 @@
                         >
                             {{ item.label }}
                         </button>
-                        <span class="ratio-label">字数</span>
-                        <button
-                            v-for="item in WRITING_WORD_COUNT_OPTIONS"
-                            :key="item.value"
-                            class="ratio-option"
-                            type="button"
-                            :class="{ 'is-active': writingWordCount === item.value }"
-                            :disabled="loading"
-                            @click="writingWordCount = item.value"
-                        >
-                            {{ item.label }}
-                        </button>
-                    </div>
-                    <div v-if="activeChatMode === 'image'" class="ratio-panel">
-                        <span class="ratio-label">图片比例</span>
-                        <button
-                            v-for="item in imageRatioOptions"
-                            :key="item.value"
-                            class="ratio-option"
-                            type="button"
-                            :class="{ 'is-active': imageRatio === item.value }"
-                            :disabled="loading"
-                            @click="imageRatio = item.value"
-                        >
-                            {{ item.label }}
-                        </button>
+                        <template v-if="writingTemplateMode">
+                            <span class="ratio-label">字数</span>
+                            <button
+                                v-for="item in WRITING_WORD_COUNT_OPTIONS"
+                                :key="item.value"
+                                class="ratio-option"
+                                type="button"
+                                :class="{ 'is-active': writingWordCount === item.value }"
+                                :disabled="loading"
+                                @click="writingWordCount = item.value"
+                            >
+                                {{ item.label }}
+                            </button>
+                        </template>
                     </div>
                     <div v-if="activeChatMode === 'image'" class="ratio-panel attach-panel">
                         <span class="ratio-label">参考素材</span>
@@ -348,11 +336,10 @@ import type { AiChatList } from "@/api/ai/aiChatList/model";
 import { sendMessage, stopMessage } from "@/api/oa/chatgpt";
 import { manuscriptGen } from "@/api/ai/manuscriptGen";
 import {
-    parseWritingRequest,
+    WRITING_DOC_TYPE_FREE,
     WRITING_DOC_TYPE_OPTIONS,
     WRITING_WORD_COUNT_OPTIONS
 } from "./writing-params";
-import type { WritingOverrides } from "./writing-params";
 import { creativeAssistant, uploadAiFile } from "@/api/ai/creativeAssistant";
 import type { CreativeAssistantUploadFile } from "@/api/ai/creativeAssistant/model";
 import { API_BASE_URL } from "@/config/setting";
@@ -404,7 +391,6 @@ const loading = ref(false);
 const stopping = ref(false);
 const content = ref("");
 const activeChatMode = ref<ChatMode>("chat");
-const imageRatio = ref("1:1");
 /**
  * 图片模式的参考素材，对应 Dify「AI 创意助手」开始节点的 file-list 变量 `user_files`。
  *
@@ -416,8 +402,8 @@ const imageRatio = ref("1:1");
 const imageFiles = ref<CreativeAttachment[]>([]);
 const uploadingFiles = ref(false);
 const fileInputRef = ref<HTMLInputElement>();
-// 写作模式的显式选择：默认 auto，即由 writing-params 从用户输入里自动识别
-const writingDocType = ref("auto");
+// 写作模式的显式选择：默认 auto = 不下发这两个字段的值，交给上游 Dify 识别
+const writingDocType = ref(WRITING_DOC_TYPE_FREE);
 const writingWordCount = ref("auto");
 const wsConnected = ref(false);
 const deletingChatId = ref<number>();
@@ -462,13 +448,9 @@ const chatModeOptions: { label: string; value: ChatMode }[] = [
     { label: "图片", value: "image" }
 ];
 
-const imageRatioOptions = [
-    { label: "1:1", value: "1:1" },
-    { label: "4:3", value: "4:3" },
-    { label: "3:4", value: "3:4" },
-    { label: "16:9", value: "16:9" },
-    { label: "9:16", value: "9:16" }
-];
+// 图片比例选择器已撤掉：上游创意助手开始节点没有比例变量（实测只有 user_content /
+// user_files），前端只能把它拼进 user_content —— 那是替上游写 prompt。
+// 要恢复这个功能，先在上游开始节点加变量，再按变量契约接上来。
 
 /** 参考素材上限，与 Dify 开始节点 user_files 的 max_length 一致 */
 const IMAGE_FILE_LIMIT = 5;
@@ -476,12 +458,17 @@ const IMAGE_FILE_EXTS = ["PNG", "JPG", "JPEG", "GIF", "WEBP", "BMP", "SVG"];
 const VIDEO_FILE_EXTS = ["MP4", "MOV", "MPEG", "MPGA", "AVI", "M4V"];
 const AUDIO_FILE_EXTS = ["MP3", "M4A", "WAV", "AMR", "AAC", "OGG", "WEBM"];
 
+/** 选中文体 = 套模板走「内容创作与宣传助手」；否则是自由创作走「AI 创意助手」 */
+const writingTemplateMode = computed(
+    () => writingDocType.value !== WRITING_DOC_TYPE_FREE
+);
+
 const inputPlaceholder = computed(() => {
     if (activeChatMode.value === "writing") {
-        return "直接描述需求即可，例如：帮我写一篇300字关于迎新晚会的推文，风格活泼，面向大一新生（也可在下方直接指定文体和字数）";
+        return "描述你想创作的内容，例如：帮我写一段迎新晚会的主持人开场词，口语化一点（选了文体后才需要再定字数）";
     }
     if (activeChatMode.value === "image") {
-        return "请输入图片生成需求，例如校园活动海报、公众号头图、志愿服务插画，并选择图片比例";
+        return "请输入图片生成需求，例如校园活动海报、公众号头图、志愿服务插画";
     }
     return "说说你想问的问题";
 });
@@ -1026,23 +1013,27 @@ const pickString = (...values: unknown[]) => {
 };
 
 const buildWritingPayload = (query: string) => {
-    // 界面上显式选了文体/字数就用显式值，否则由 writing-params 从自然语言里识别。
-    // 过去这里没有表单，一律回落 doc_type=新闻稿 / Number=800，而上游提示词把这两项
-    // 当作主控指令，会直接压掉用户原话里的诉求（实测见 .scratch/ai-assistant/probe/）。
-    const overrides: WritingOverrides = {};
-    if (writingDocType.value !== "auto") {
-        overrides.docType = writingDocType.value;
+    // 两条路，都不解析自然语言（2026-10-21 改造）：
+    // - 自由创作：原话整段作为 userContent，后端见 docType 为空就转「AI 创意助手」；
+    // - 选了文体：原话整段作为 highlights，只带界面显式选过的 docType / number，
+    //   其余可选字段留空交给上游。doc_type / Number 是上游提示词的**主控指令**，
+    //   本地猜会猜错（见 issue 13）。
+    const content = String(query || "").trim();
+    if (writingDocType.value === WRITING_DOC_TYPE_FREE) {
+        return { docType: "", userContent: content };
     }
-    if (writingWordCount.value !== "auto") {
-        overrides.number = Number(writingWordCount.value);
-    }
-    return {
-        ...parseWritingRequest(query, overrides),
+    const payload: Record<string, unknown> = {
+        docType: writingDocType.value,
+        highlights: content,
         files: []
     };
+    if (writingWordCount.value !== "auto") {
+        payload.number = Number(writingWordCount.value);
+    }
+    return payload;
 };
 
-const formatWritingResult = (payload: unknown, query: string) => {
+const formatWritingResult = (payload: unknown) => {
     if (typeof payload === "string") {
         return payload;
     }
@@ -1076,7 +1067,9 @@ const formatWritingResult = (payload: unknown, query: string) => {
         data.choices?.[0]?.message?.content
     );
     if (title || body) {
-        return `${title || buildWritingPayload(query).theme}\n\n${body}`;
+        // 不再从入参里补标题：改造后没有「从原话抽主题」这一步，
+        // 拼一个空标题只会在正文前多两行空行。
+        return title ? `${title}\n\n${body}` : body;
     }
     // 不再 stringifyUnknown(payload)：那会把 conversationId / taskId 这类
     // 内部标识符整包渲染给用户。
@@ -1222,14 +1215,6 @@ const formatCreativeResult = (payload: unknown) => {
     });
 };
 
-const buildImagePrompt = (query: string) => {
-    return [
-        query,
-        `图片比例：${imageRatio.value}`,
-        "请直接生成图片，优先输出图片文件或图片链接。"
-    ].join("\n");
-};
-
 /** 按 MIME 或扩展名判定 Dify file-list 要求的 type（image/video/audio/document） */
 const resolveUploadFileType = (
     contentType: string,
@@ -1309,7 +1294,13 @@ const onImageFilesPicked = async (event: Event) => {
     }
 };
 
-/** 图片模式入参：user_content 一段文本 + user_files（Dify file-list 变量） */
+/**
+ * 图片模式入参：`user_content` 就是**用户原话** + `user_files`（Dify file-list 变量）。
+ *
+ * 不往 `user_content` 里追加任何我们自己写的话（如「图片比例：1:1」
+ * 「请直接生成图片…」）：上游创意助手只有 `user_content` / `user_files` 两个变量，
+ * 没有比例变量，拼进去等于替上游写 prompt。比例选择器已撤掉。
+ */
 const buildImagePayload = (query: string) => {
     const userFiles: CreativeAssistantUploadFile[] = imageFiles.value.map((item) => ({
         transfer_method: "local_file",
@@ -1318,7 +1309,7 @@ const buildImagePayload = (query: string) => {
         url: ""
     }));
     return {
-        user_content: buildImagePrompt(query),
+        user_content: query,
         user_files: userFiles
     };
 };
@@ -1340,7 +1331,7 @@ const sendModeMessage = async (
         if (typeof (result as any)?.taskId === "string") {
             currentTaskId.value = (result as any).taskId;
         }
-        setResult(formatWritingResult(result, query));
+        setResult(formatWritingResult(result));
         return;
     }
     if (activeChatMode.value === "image") {