feat: add containerization support

- Add Containerfile with multi-stage build for minimal image
- Add .containerignore to exclude unnecessary files
- Add /health endpoint for container health checks
- Update main.py to expose Flask app for gunicorn

Uses Python 3.12-slim base, runs as non-root user, exposes port 8000.

src/routes/setup.py

@@ -1,6 +1,6 @@
 """Setup route for initial admin account creation."""
 
-from flask import Blueprint, abort, redirect, render_template, session, url_for
+from flask import Blueprint, abort, jsonify, redirect, render_template, session, url_for
 
 from src.app import bcrypt, db
 from src.forms import SetupForm
@@ -9,6 +9,21 @@ from src.models import Admin
 setup_bp = Blueprint("setup", __name__)
 
 
+@setup_bp.route("/health")
+def health():
+    """Health check endpoint for container orchestration.
+
+    Returns:
+        JSON response with health status.
+    """
+    try:
+        # Check database connectivity
+        db.session.execute(db.text("SELECT 1"))
+        return jsonify({"status": "healthy", "database": "connected"}), 200
+    except Exception as e:
+        return jsonify({"status": "unhealthy", "error": str(e)}), 503
+
+
 @setup_bp.route("/setup", methods=["GET", "POST"])
 def setup():
     """Handle initial admin account setup.