fix: resolve database and session initialization issues

- Switch from SQLAlchemy sessions to filesystem sessions to avoid race
  conditions with multiple gunicorn workers trying to create the sessions
  table simultaneously
- Update Alembic env.py to use a minimal Flask app without Flask-Session
  to prevent session table creation during migrations
- Add data directory creation to entrypoint.sh for clean container starts
- Configure test environment to use filesystem sessions with temp directory

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

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

src/config.py

@@ -25,8 +25,9 @@ class Config:
     )
     SQLALCHEMY_TRACK_MODIFICATIONS = False
 
-    # Session management
-    SESSION_TYPE = "sqlalchemy"
+    # Session management (filesystem-based to avoid race conditions with SQLAlchemy)
+    SESSION_TYPE = "filesystem"
+    SESSION_FILE_DIR = DATA_DIR / "sessions"
     SESSION_PERMANENT = True
     SESSION_USE_SIGNER = True
     SESSION_KEY_PREFIX = "sk:"
@@ -90,6 +91,10 @@ class TestConfig(Config):
     # Use in-memory database for tests
     SQLALCHEMY_DATABASE_URI = "sqlite:///:memory:"
 
+    # Use filesystem session with temp directory for tests
+    SESSION_TYPE = "filesystem"
+    SESSION_FILE_DIR = Path("/tmp/sneaky-klaus-test-sessions")
+
     # Disable CSRF for easier testing
     WTF_CSRF_ENABLED = False