Add multi-user support: Authelia OIDC, SQLite, Garage S3

- Auth via Authelia OIDC (public client + PKCE) with signed session cookies
- SQLite DB for users, rides, and insights (SQLAlchemy)
- Garage S3 for GPX file storage (boto3)
- All API endpoints scoped to authenticated user
- Dockerfile + docker-compose.yml with Garage service
- Frontend auth check: redirects to /auth/login on 401, shows user badge

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -0,0 +1,30 @@
+services:
+  bikeslop:
+    build: .
+    restart: unless-stopped
+    ports:
+      - "8000:8000"
+    env_file: .env
+    environment:
+      DATABASE_URL: sqlite:////data/bikeslop.db
+    volumes:
+      - ./data:/data
+    depends_on:
+      - garage
+
+  garage:
+    image: dxflrs/garage:v2.2.0
+    restart: unless-stopped
+    ports:
+      - "3900:3900"
+      - "3901:3901"
+      - "3902:3902"
+      - "3903:3903"
+    volumes:
+      - ./garage.toml:/etc/garage.toml:ro
+      - garage-meta:/var/lib/garage/meta
+      - garage-data:/var/lib/garage/data
+
+volumes:
+  garage-meta:
+  garage-data: