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>

migrations/env.py

@@ -4,12 +4,13 @@ This module configures Alembic to work with the Flask application
 and SQLAlchemy models.
 """
 
+import os
 from logging.config import fileConfig
+from pathlib import Path
 
 from alembic import context
-
-# Import Flask app and database before configuring Alembic
-from src.app import create_app, db
+from flask import Flask
+from flask_sqlalchemy import SQLAlchemy
 
 # this is the Alembic Config object, which provides
 # access to the values within the .ini file in use.
@@ -20,8 +21,31 @@ config = context.config
 if config.config_file_name is not None:
     fileConfig(config.config_file_name)
 
-# Configure database URL from Flask config
-app = create_app()
+# Create minimal Flask app for migrations (without session initialization)
+# This avoids Flask-Session trying to create tables before migrations run
+app = Flask(__name__)
+BASE_DIR = Path(__file__).parent.parent
+DATA_DIR = BASE_DIR / "data"
+DATA_DIR.mkdir(parents=True, exist_ok=True)
+
+app.config["SQLALCHEMY_DATABASE_URI"] = os.environ.get(
+    "DATABASE_URL", f"sqlite:///{DATA_DIR / 'sneaky-klaus.db'}"
+)
+app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
+
+db = SQLAlchemy()
+db.init_app(app)
+
+# Import all models to register them with SQLAlchemy metadata
+with app.app_context():
+    from src.models import (  # noqa: F401
+        Admin,
+        Exchange,
+        MagicToken,
+        Participant,
+        RateLimit,
+    )
+
 config.set_main_option("sqlalchemy.url", app.config["SQLALCHEMY_DATABASE_URI"])
 
 # Add your model's MetaData object here for 'autogenerate' support