Fix UNIQUE constraint error in get_or_create_user_account

Handles race condition where user account already exists from initial sync
but without user_id set. When user configures wallet, code now:
- Catches IntegrityError on UNIQUE constraint for accounts.name
- Fetches existing account by name
- Updates user_id if NULL or different
- Returns existing account instead of failing

This fixes the error that occurred when users configured their wallet after
their accounts were created during the initial Beancount sync.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

crud.py

@@ -283,6 +283,7 @@ async def get_or_create_user_account(
             logger.error(f"[CASTLE DB] Account still not found after sync: {account_name}")
             # Fallback: create directly in Castle DB if sync failed
             logger.info(f"[CASTLE DB] Creating account directly in Castle DB: {account_name}")
+            try:
                 account = await create_account(
                     CreateAccount(
                         name=account_name,
@@ -291,6 +292,44 @@ async def get_or_create_user_account(
                         user_id=user_id,
                     )
                 )
+            except Exception as e:
+                # Handle UNIQUE constraint error - account already exists
+                if "UNIQUE constraint failed" in str(e) and "accounts.name" in str(e):
+                    logger.warning(f"[CASTLE DB] Account already exists (UNIQUE constraint), fetching by name: {account_name}")
+                    # Fetch existing account by name only (ignore user_id in query)
+                    account = await db.fetchone(
+                        """
+                        SELECT * FROM accounts
+                        WHERE name = :name
+                        """,
+                        {"name": account_name},
+                        Account,
+                    )
+                    if account:
+                        logger.info(f"[CASTLE DB] Found existing account: {account_name} (user_id: {account.user_id})")
+                        # Update user_id if it's NULL or different
+                        if account.user_id != user_id:
+                            logger.info(f"[CASTLE DB] Updating account user_id from {account.user_id} to {user_id}")
+                            await db.execute(
+                                """
+                                UPDATE accounts
+                                SET user_id = :user_id
+                                WHERE name = :name
+                                """,
+                                {"user_id": user_id, "name": account_name}
+                            )
+                            # Refresh account from DB
+                            account = await db.fetchone(
+                                """
+                                SELECT * FROM accounts
+                                WHERE name = :name
+                                """,
+                                {"name": account_name},
+                                Account,
+                            )
+                else:
+                    # Re-raise if it's a different error
+                    raise
     else:
         logger.info(f"[CASTLE DB] Account already exists in Castle DB: {account_name}")