feat: implement Phase 2 core features

- Add document CRUD API (list/get/upload/update/delete with auth)
  - Upload saves to Inbox + auto-enqueues processing pipeline
  - Delete defaults to DB-only, explicit flag for file deletion
- Add hybrid search API (FTS 0.4 + trigram 0.2 + vector 0.4 weighted)
  - Modes: fts, trgm, vector, hybrid (default)
  - Vector search gracefully degrades if GPU unavailable
- Add Inbox file watcher (5min interval, new file + hash change detection)
- Register documents/search routers and file_watcher scheduler in main.py
- Add IVFFLAT vector index migration (lists=50, with tuning guide)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/workers/file_watcher.py

@@ -0,0 +1,97 @@
+"""파일 감시 워커 — Inbox 디렉토리 스캔, 새 파일/변경 파일 자동 등록"""
+
+from pathlib import Path
+
+from sqlalchemy import select
+
+from core.config import settings
+from core.database import async_session
+from core.utils import file_hash, setup_logger
+from models.document import Document
+from models.queue import ProcessingQueue
+
+logger = setup_logger("file_watcher")
+
+# 무시할 파일
+SKIP_NAMES = {".DS_Store", "Thumbs.db", "desktop.ini", "Icon\r"}
+SKIP_EXTENSIONS = {".tmp", ".part", ".crdownload"}
+
+
+def should_skip(path: Path) -> bool:
+    if path.name in SKIP_NAMES or path.name.startswith("._"):
+        return True
+    if path.suffix.lower() in SKIP_EXTENSIONS:
+        return True
+    return False
+
+
+async def watch_inbox():
+    """Inbox 디렉토리를 스캔하여 새/변경 파일을 DB에 등록"""
+    inbox_path = Path(settings.nas_mount_path) / "PKM" / "Inbox"
+    if not inbox_path.exists():
+        return
+
+    files = [f for f in inbox_path.rglob("*") if f.is_file() and not should_skip(f)]
+    if not files:
+        return
+
+    new_count = 0
+    changed_count = 0
+
+    async with async_session() as session:
+        for file_path in files:
+            rel_path = str(file_path.relative_to(Path(settings.nas_mount_path)))
+            fhash = file_hash(file_path)
+
+            # DB에서 기존 문서 확인
+            result = await session.execute(
+                select(Document).where(Document.file_path == rel_path)
+            )
+            existing = result.scalar_one_or_none()
+
+            if existing is None:
+                # 새 파일 → 등록
+                ext = file_path.suffix.lstrip(".").lower() or "unknown"
+                doc = Document(
+                    file_path=rel_path,
+                    file_hash=fhash,
+                    file_format=ext,
+                    file_size=file_path.stat().st_size,
+                    file_type="immutable",
+                    title=file_path.stem,
+                    source_channel="drive_sync",
+                )
+                session.add(doc)
+                await session.flush()
+
+                session.add(ProcessingQueue(
+                    document_id=doc.id,
+                    stage="extract",
+                    status="pending",
+                ))
+                new_count += 1
+
+            elif existing.file_hash != fhash:
+                # 해시 변경 → 재가공
+                existing.file_hash = fhash
+                existing.file_size = file_path.stat().st_size
+
+                # 기존 pending/processing 큐 항목이 없으면 extract부터 재시작
+                queue_check = await session.execute(
+                    select(ProcessingQueue).where(
+                        ProcessingQueue.document_id == existing.id,
+                        ProcessingQueue.status.in_(["pending", "processing"]),
+                    )
+                )
+                if not queue_check.scalar_one_or_none():
+                    session.add(ProcessingQueue(
+                        document_id=existing.id,
+                        stage="extract",
+                        status="pending",
+                    ))
+                changed_count += 1
+
+        await session.commit()
+
+    if new_count or changed_count:
+        logger.info(f"[Inbox] 새 파일 {new_count}건, 변경 파일 {changed_count}건 등록")