feat: 知识库笔记工坊立项 + contributor 功能 + Fable5 视角文档

- 知识库笔记工坊子项目立项：PRD v1.0 + 寄存条 + CLAUDE.md 登记
- 后端：知识库上传记录 contributor、新增 /contributors 接口
- 前端：知识库列表支持按贡献人筛选
- 新增 Fable5 视角模式库/案例集/建议文档

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/api/knowledge.py

@@ -37,7 +37,7 @@ async def upload_md_files(
             continue
         try:
             content = await f.read()
-            item = svc.store_md_file(content, f.filename)
+            item = svc.store_md_file(content, f.filename, contributor=current_user.display_name or current_user.username)
             results.append({
                 "id": item.id,
                 "title": item.title,
@@ -93,6 +93,16 @@ def list_distinct_sources(
     return [{"source": s} for s in sources]
 
 
+@router.get("/contributors")
+def list_distinct_contributors(
+    session: Session = Depends(get_session),
+    current_user: User = Depends(require_role(UserRole.zhipianren, UserRole.zebian, UserRole.biandao)),
+):
+    svc = KnowledgeService()
+    contributors = svc.get_distinct_contributors()
+    return [{"contributor": c} for c in contributors]
+
+
 @router.get("/grouped")
 def get_grouped_knowledge_items(
     session: Session = Depends(get_session),