Fix SQLite database locking under concurrent access

Add busy_timeout (5 seconds) to both async and sync database connections.
This prevents "database is locked" errors when multiple requests try to
access the database simultaneously.

Changes:
- AsyncSQLitePool: Add busy_timeout=5000 and synchronous=NORMAL pragmas
- DatabaseCache: Add WAL mode, busy_timeout, synchronous=NORMAL, and
  connection timeout for the sync database module

The busy_timeout tells SQLite to wait instead of immediately failing
when the database is locked by another connection.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/exchange_data_manager/cache/connection_pool.py

@@ -76,6 +76,11 @@ class AsyncSQLitePool:
         conn = await aiosqlite.connect(self.db_path)
         # Enable WAL mode for better concurrent read/write performance
         await conn.execute("PRAGMA journal_mode=WAL")
+        # Set busy timeout to wait up to 5 seconds when database is locked
+        # This prevents "database is locked" errors during concurrent access
+        await conn.execute("PRAGMA busy_timeout=5000")
+        # Use NORMAL synchronous mode with WAL for good performance + durability
+        await conn.execute("PRAGMA synchronous=NORMAL")
         # Enable foreign keys
         await conn.execute("PRAGMA foreign_keys=ON")
         return conn

src/exchange_data_manager/cache/database.py

@@ -73,8 +73,14 @@ class DatabaseCache:
     @contextmanager
     def _get_connection(self):
         """Get a database connection with proper cleanup."""
-        conn = sqlite3.connect(self.db_path)
+        conn = sqlite3.connect(self.db_path, timeout=5.0)
         conn.row_factory = sqlite3.Row
+        # Enable WAL mode for better concurrent read/write performance
+        conn.execute("PRAGMA journal_mode=WAL")
+        # Set busy timeout to wait when database is locked (in addition to connect timeout)
+        conn.execute("PRAGMA busy_timeout=5000")
+        # Use NORMAL synchronous mode with WAL for good performance + durability
+        conn.execute("PRAGMA synchronous=NORMAL")
         try:
             yield conn
         finally: