Browse the knowledge base from a single side panel menu

Add a read-only view of backend/knowledge_base/**.md so the files that get
injected into the system prompt can be inspected from the GUI:

- GET /api/kb/files lists the Markdown files (title, preview, size, mtime and
  whether the file is already embedded), GET /api/kb/file returns one in full.
  Paths are resolved against the knowledge base directory and rejected unless
  they stay inside it and end in .md.
- KnowledgeBasePanel.vue groups the files by folder (collapsible, so web_search
  can be folded away), filters by title/path/preview and renders the selected
  file with MarkdownContent.

The header had grown to four side panel toggles, so collapse them into one
menu: panels.ts now holds the list of panels along with the component each one
renders, App.vue picks it with <component :is>, and SidePanelMenu.vue shows the
active panel on its button. Re-picking the open panel (or "パネルを閉じる")
closes it; a click outside or Esc closes just the menu.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/app/api/knowledge_base.py

@@ -0,0 +1,61 @@
+"""ローカルナレッジベース（backend/knowledge_base/**.md）を GUI から閲覧するための読み取り専用 API。
+
+コンテキスト注入に使われるファイルそのものを一覧・表示するだけで、ここからの編集はできない。
+埋め込み済みかどうか（indexed）は local_knowledge_docs テーブルを引いて付ける。
+"""
+from datetime import datetime
+
+from fastapi import APIRouter, Depends, HTTPException, Query
+from pydantic import BaseModel
+from sqlalchemy.orm import Session as DBSession
+
+from app.core.memory_kb.local_knowledge import list_kb_files, read_kb_file
+from app.db.database import get_db
+from app.db.models import LocalKnowledgeDoc
+
+router = APIRouter(prefix="/api/kb", tags=["knowledge-base"])
+
+
+class KbFileInfo(BaseModel):
+    path: str
+    name: str
+    # ナレッジベース直下のファイルは空文字。UI ではこの単位でグループ表示する
+    directory: str
+    title: str
+    preview: str
+    size: int
+    updated_at: datetime
+    # 埋め込み済み（＝話題に応じた自動注入の対象になっている）か
+    indexed: bool
+
+
+class KbFileContent(BaseModel):
+    path: str
+    name: str
+    title: str
+    content: str
+    size: int
+    updated_at: datetime
+
+
+@router.get("/files", response_model=list[KbFileInfo])
+def list_files(db: DBSession = Depends(get_db)):
+    """ナレッジベース配下の Markdown を一覧で返す（本文は含めず、先頭のプレビューのみ）。"""
+    indexed_paths = {
+        # DB 側は OS 依存の区切り文字で保存されているため、比較用に posix 形式へ寄せる
+        path.replace("\\", "/")
+        for (path,) in db.query(LocalKnowledgeDoc.path).all()
+    }
+    return [
+        KbFileInfo(**info, indexed=info["path"] in indexed_paths)
+        for info in list_kb_files()
+    ]
+
+
+@router.get("/file", response_model=KbFileContent)
+def get_file(path: str = Query(..., description="ナレッジベースディレクトリからの相対パス")):
+    """1ファイルの全文を返す。"""
+    file = read_kb_file(path)
+    if file is None:
+        raise HTTPException(status_code=404, detail="Knowledge base file not found")
+    return KbFileContent(**file)