feat: [US-001] Add automatic Alembic migrations at backend startup

- Add alembic.ini config for data_entry module
- Add migrations.py helper with:
  - run_migrations(): runs pending migrations at startup (returns True/False)
  - get_current_revision(): returns current schema version for /health
- Integrate migrations in main.py startup_event() BEFORE init_data_entry_db()
- Add data_entry_schema_version to /health endpoint

If migrations fail, backend continues with WARNING (not crash).

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

backend/modules/data_entry/db/migrations.py

@@ -0,0 +1,131 @@
+"""
+Alembic migrations helper for Data Entry module.
+
+Provides automatic migration execution at backend startup.
+"""
+
+import logging
+import os
+from pathlib import Path
+
+logger = logging.getLogger(__name__)
+
+
+def run_migrations() -> bool:
+    """
+    Run pending Alembic migrations at startup.
+
+    Returns:
+        True if migrations ran successfully (or no pending migrations),
+        False if migrations failed (backend should continue with WARNING).
+    """
+    try:
+        from alembic.config import Config
+        from alembic import command
+        from alembic.runtime.migration import MigrationContext
+        from sqlalchemy import create_engine
+
+        # Get the path to alembic.ini
+        data_entry_module = Path(__file__).parent.parent
+        alembic_ini_path = data_entry_module / "alembic.ini"
+
+        if not alembic_ini_path.exists():
+            logger.warning(f"[MIGRATIONS] alembic.ini not found at {alembic_ini_path}")
+            return False
+
+        # Get database path from environment or default
+        db_path = Path(os.getenv(
+            "SQLITE_DATABASE_PATH",
+            "data/receipts/receipts.db"
+        )).resolve()
+
+        # Ensure database directory exists
+        db_path.parent.mkdir(parents=True, exist_ok=True)
+
+        # Create Alembic config
+        alembic_cfg = Config(str(alembic_ini_path))
+
+        # Override database URL
+        sync_db_url = f"sqlite:///{db_path}"
+        alembic_cfg.set_main_option("sqlalchemy.url", sync_db_url)
+
+        # Set script location relative to alembic.ini
+        alembic_cfg.set_main_option(
+            "script_location",
+            str(data_entry_module / "migrations")
+        )
+
+        # Get current revision before upgrade
+        engine = create_engine(sync_db_url)
+        with engine.connect() as connection:
+            context = MigrationContext.configure(connection)
+            current_rev = context.get_current_revision()
+        engine.dispose()
+
+        logger.info(f"[MIGRATIONS] Current revision: {current_rev or 'None (fresh database)'}")
+        logger.info(f"[MIGRATIONS] Database path: {db_path}")
+
+        # Run upgrade to head
+        logger.info("[MIGRATIONS] Checking for pending migrations...")
+        command.upgrade(alembic_cfg, "head")
+
+        # Get new revision after upgrade
+        engine = create_engine(sync_db_url)
+        with engine.connect() as connection:
+            context = MigrationContext.configure(connection)
+            new_rev = context.get_current_revision()
+        engine.dispose()
+
+        if current_rev != new_rev:
+            logger.info(f"[MIGRATIONS] Applied: {current_rev or 'None'} -> {new_rev}")
+        else:
+            logger.info(f"[MIGRATIONS] No pending migrations. Current: {new_rev}")
+
+        return True
+
+    except ImportError as e:
+        logger.warning(f"[MIGRATIONS] Alembic not installed: {e}")
+        logger.warning("[MIGRATIONS] Skipping migrations - install alembic to enable")
+        return False
+
+    except Exception as e:
+        logger.error(f"[MIGRATIONS] Migration error: {e}", exc_info=True)
+        logger.warning("[MIGRATIONS] Backend will continue without migrations")
+        return False
+
+
+def get_current_revision() -> str:
+    """
+    Get the current Alembic revision.
+
+    Returns:
+        Current revision string, or 'unknown' if cannot be determined.
+    """
+    try:
+        from alembic.runtime.migration import MigrationContext
+        from sqlalchemy import create_engine
+
+        # Get database path from environment or default
+        db_path = Path(os.getenv(
+            "SQLITE_DATABASE_PATH",
+            "data/receipts/receipts.db"
+        )).resolve()
+
+        if not db_path.exists():
+            return "no_database"
+
+        sync_db_url = f"sqlite:///{db_path}"
+        engine = create_engine(sync_db_url)
+
+        with engine.connect() as connection:
+            context = MigrationContext.configure(connection)
+            revision = context.get_current_revision()
+
+        engine.dispose()
+        return revision or "none"
+
+    except ImportError:
+        return "alembic_not_installed"
+    except Exception as e:
+        logger.debug(f"[MIGRATIONS] Could not get revision: {e}")
+        return "unknown"