feat: REST API + Web-Frontend für Kalenderübersicht

- FastAPI Backend mit /api/events, /api/events/{id}, /api/health Endpoints
- Optionale Suche nach Event-Titel (Query Parameter ?search=...)
- Jinja2 Web-Frontend auf / mit Suchfeld
- Shared DB Connection Module (api/database.py)
- Docker Compose: calendar-api Service hinzugefügt
- Sync.py refactored: nutzt shared database.py

api/database.py

@@ -0,0 +1,19 @@
+import os
+import mysql.connector
+
+DB_HOST = os.environ.get("DB_HOST", "mariadb.fritz.box")
+DB_PORT = int(os.environ.get("DB_PORT", "3306"))
+DB_NAME = os.environ.get("DB_NAME", "calendar_sync")
+DB_USER = os.environ["DB_USER"]
+DB_PASSWORD = os.environ["DB_PASSWORD"]
+
+
+def get_connection(autocommit: bool = True):
+    return mysql.connector.connect(
+        host=DB_HOST,
+        port=DB_PORT,
+        user=DB_USER,
+        password=DB_PASSWORD,
+        database=DB_NAME,
+        autocommit=autocommit,
+    )