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/core/memory_kb/local_knowledge.py

@@ -8,6 +8,7 @@ import json
 import logging
 import math
 import os
+from datetime import datetime, timezone
 from pathlib import Path
 
 from sqlalchemy.orm import Session as DBSession
@@ -174,3 +175,79 @@ async def get_local_kb_context(db: DBSession, query_text: str) -> str | None:
         "ここに必要な情報が含まれている場合はWeb検索を行わず、この内容のみで回答してください。"
         "情報が不足する場合に限り、補足としてWeb検索を使ってください:\n\n" + "\n\n".join(blocks)
     )
+
+
+# --- GUI からの閲覧用（埋め込みやコンテキスト注入とは無関係の、ファイルブラウズ機能） ---
+
+# 一覧のタイトル・プレビュー生成のために読む先頭バイト数（全文を読まずに済ませるため）
+_PREVIEW_READ_CHARS = 2000
+
+
+def _preview_from_content(content: str) -> str:
+    """本文から見出し・空行を除いた最初の行を、一覧に出すプレビューとして切り出す。"""
+    for line in content.splitlines():
+        stripped = line.strip()
+        if stripped and not stripped.startswith("#"):
+            return stripped[:120]
+    return ""
+
+
+def resolve_kb_path(rel_path: str) -> Path | None:
+    """ブラウザから渡された相対パスを実ファイルに解決する。
+
+    ナレッジベースディレクトリの外を指すパス（`../` など）や .md 以外は None を返す。
+    """
+    root = _kb_dir().resolve()
+    try:
+        target = (root / rel_path).resolve()
+    except OSError:
+        return None
+    if not target.is_relative_to(root) or target.suffix.lower() != ".md":
+        return None
+    return target if target.is_file() else None
+
+
+def list_kb_files() -> list[dict]:
+    """ナレッジベース配下の Markdown を一覧にする。本文は先頭だけ読む。"""
+    root = _kb_dir()
+    if not root.is_dir():
+        return []
+
+    files = []
+    for file_path in sorted(root.rglob("*.md")):
+        rel_path = file_path.relative_to(root)
+        try:
+            stat = file_path.stat()
+            with file_path.open(encoding="utf-8", errors="replace") as f:
+                head = f.read(_PREVIEW_READ_CHARS)
+        except OSError:
+            logger.exception("Failed to read local knowledge file: %s", rel_path)
+            continue
+        files.append({
+            "path": rel_path.as_posix(),
+            "name": file_path.name,
+            "directory": rel_path.parent.as_posix() if rel_path.parent != Path(".") else "",
+            "title": _title_from_content(head, fallback=file_path.stem),
+            "preview": _preview_from_content(head),
+            "size": stat.st_size,
+            "updated_at": datetime.fromtimestamp(stat.st_mtime, tz=timezone.utc),
+        })
+    return files
+
+
+def read_kb_file(rel_path: str) -> dict | None:
+    """1ファイルの全文を返す。パスが不正・存在しない場合は None。"""
+    target = resolve_kb_path(rel_path)
+    if target is None:
+        return None
+    content = target.read_text(encoding="utf-8", errors="replace")
+    stat = target.stat()
+    normalized = target.resolve().relative_to(_kb_dir().resolve()).as_posix()
+    return {
+        "path": normalized,
+        "name": target.name,
+        "title": _title_from_content(content, fallback=target.stem),
+        "content": content,
+        "size": stat.st_size,
+        "updated_at": datetime.fromtimestamp(stat.st_mtime, tz=timezone.utc),
+    }