fix(ai): 写作入口采集上游主控字段，用户诉求不再被默认值覆盖（issue 13）

聊天页「写作」模式没有表单，只按「键：值」解析输入，普通自然语言解析为空后一律回落
doc_type=新闻稿 / Number=800。上游「AI内容创作与宣传助手」的 prompt 把这两项当主控指令，
实测模型会主动忽略用户原话里的冲突要求，思维链原文：

  I will ignore the conflicting "300字推文" instruction inside the bullet points
  because the main task says "文稿类型为：新闻稿" and "篇幅要求（字数限制）：800"

这就是用户报的「写作模块听不懂要求」——不是模型听不懂，是把「新闻稿/800字」当硬指令发给了它。

- 新增 src/views/oa/chatgpt/writing-params.ts：从自然语言抽取文体/字数/主题/时间/地点/
  人员/活动类型，保留既有「键：值」入参，界面显式选择优先于自动识别；纯函数零依赖，
  可直接用 node 运行测试
- 文体识别对齐上游真实存在的 4 个模板（新闻稿/活动总结/微信推文/通知公告）；认不出的文体
  （发言稿、短视频脚本等）原样下发交给模型发挥，强行映射成新闻稿会更糟
- 用户没提字数时按文体给常规篇幅，而不是不下发——上游对空字数的处理会在正文里留一行
  「（未设定有效字数限制）」
- 写作模式输入框上方新增「文体 / 字数」两组按钮，复用既有 ratio-panel 样式

验证：解析用例 8/8（.scratch/ai-assistant/probe/test-writing-params.ts）；同一句输入做端到端
对照，修复前得 800 字新闻稿，修复后得 281 字微信推文（引用块 + ## 模块小标题 + 【互动时间】）。

src/views/oa/chatgpt/index.vue

@@ -213,6 +213,32 @@
                     <span>{{ assistantTitle }}</span>
                 </div>
                 <div class="input-shell">
+                    <div v-if="activeChatMode === 'writing'" class="ratio-panel">
+                        <span class="ratio-label">文体</span>
+                        <button
+                            v-for="item in WRITING_DOC_TYPE_OPTIONS"
+                            :key="item.value"
+                            class="ratio-option"
+                            type="button"
+                            :class="{ 'is-active': writingDocType === item.value }"
+                            :disabled="loading"
+                            @click="writingDocType = item.value"
+                        >
+                            {{ 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
@@ -316,6 +342,12 @@ import { listAiChatList, removeAiChatList } from "@/api/ai/aiChatList";
 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_OPTIONS,
+    WRITING_WORD_COUNT_OPTIONS
+} from "./writing-params";
+import type { WritingOverrides } from "./writing-params";
 import { creativeAssistant } from "@/api/ai/creativeAssistant";
 import { API_BASE_URL } from "@/config/setting";
 import type { Menu } from "@/api/system/menu/model";
@@ -360,6 +392,9 @@ const stopping = ref(false);
 const content = ref("");
 const activeChatMode = ref<ChatMode>("chat");
 const imageRatio = ref("1:1");
+// 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");
+const writingWordCount = ref("auto");
 const wsConnected = ref(false);
 const deletingChatId = ref<number>();
 const messages = ref<ChatMessageItem[]>([]);
@@ -413,7 +448,7 @@ const imageRatioOptions = [
 
 const inputPlaceholder = computed(() => {
     if (activeChatMode.value === "writing") {
-        return "请输入写作需求，例如新闻稿、推文文案、小论文、发言稿，也可以补充标题、受众、字数和风格";
+        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）";
     }
     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";
@@ -960,32 +995,19 @@ const pickString = (...values: unknown[]) => {
     return "";
 };
 
-const parseKeyValueInput = (value: string) => {
-    const result: Record<string, string> = {};
-    value
-        .split(/\n+/)
-        .map((item) => item.trim())
-        .filter(Boolean)
-        .forEach((line) => {
-            const match = line.match(/^([^:：]+)[:：]\s*(.*)$/);
-            if (match) {
-                result[match[1].trim()] = match[2].trim();
-            }
-        });
-    return result;
-};
-
 const buildWritingPayload = (query: string) => {
-    const fields = parseKeyValueInput(query);
+    // 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;
+    }
+    if (writingWordCount.value !== "auto") {
+        overrides.number = Number(writingWordCount.value);
+    }
     return {
-        docType: fields["稿件类型"] || fields["文体"] || fields["类型"] || "新闻稿",
-        eventType: fields["活动类型"] || fields["场景"] || "校园内容",
-        theme: fields["稿件标题"] || fields["标题"] || fields["主题"] || query,
-        time: fields["活动时间"] || fields["时间"] || "",
-        location: fields["活动地点"] || fields["地点"] || "",
-        participants: fields["参与人员"] || fields["受众"] || fields["人员"] || "",
-        highlights: fields["亮点内容"] || fields["要点"] || fields["亮点"] || fields["内容"] || query,
-        number: Number(fields["建议篇幅"] || fields["字数"] || 800),
+        ...parseWritingRequest(query, overrides),
         files: []
     };
 };