Add PostgreSQL production backend to eliminate SQLite lock contention.

Support DATABASE_URL with connection pooling, pg_dump backups, SQLite migration script, and deploy_postgres.sh with docs.

Co-authored-by: Cursor <cursoragent@cursor.com>

ai_messages.py

@@ -7,9 +7,8 @@
 from __future__ import annotations
 
 import json
-import sqlite3
 from datetime import datetime
-from typing import Any, Callable, Optional
+from typing import Any, Optional
 from zoneinfo import ZoneInfo
 
 TZ = ZoneInfo("Asia/Shanghai")
@@ -26,7 +25,7 @@ CREATE TABLE IF NOT EXISTS ai_messages (
 """
 
 
-def ensure_ai_messages_table(conn: sqlite3.Connection) -> None:
+def ensure_ai_messages_table(conn) -> None:
     conn.execute(CREATE_SQL)
     conn.execute(
         "CREATE INDEX IF NOT EXISTS idx_ai_messages_created ON ai_messages(created_at DESC)"
@@ -34,7 +33,7 @@ def ensure_ai_messages_table(conn: sqlite3.Connection) -> None:
 
 
 def insert_ai_message(
-    conn: sqlite3.Connection,
+    conn,
     *,
     kind: str,
     title: str,
@@ -45,13 +44,16 @@ def insert_ai_message(
     now = datetime.now(TZ).strftime("%Y-%m-%d %H:%M:%S")
     cur = conn.execute(
         """INSERT INTO ai_messages (kind, title, content, meta_json, created_at)
-           VALUES (?,?,?,?,?)""",
+           VALUES (?,?,?,?,?) RETURNING id""",
         (kind, title, content, json.dumps(meta or {}, ensure_ascii=False), now),
     )
-    return int(cur.lastrowid)
+    row = cur.fetchone()
+    if row is not None:
+        return int(row["id"] if isinstance(row, dict) else row[0])
+    return int(cur.lastrowid or 0)
 
 
-def list_ai_messages(conn: sqlite3.Connection, *, limit: int = 100) -> list[dict]:
+def list_ai_messages(conn, *, limit: int = 100) -> list[dict]:
     ensure_ai_messages_table(conn)
     rows = conn.execute(
         "SELECT * FROM ai_messages ORDER BY id DESC LIMIT ?",