Add oidc-provider-mock dev setup with docker-compose and dotenvy

- docker-compose.yml runs oidc-provider-mock on :9400 with predefined
  alice/bob users carrying preferred_username claims
- .env auto-loaded via dotenvy for zero-config local dev
- index route now redirects unauthenticated users to the login flow
  instead of returning 401

docker-compose.yml

@@ -0,0 +1,10 @@
+services:
+  oidc:
+    image: ghcr.io/geigerzaehler/oidc-provider-mock:latest
+    ports:
+      - "9400:9400"
+    command:
+      - --user-claims
+      - '{"sub": "alice", "preferred_username": "alice", "email": "alice@example.com", "name": "Alice"}'
+      - --user-claims
+      - '{"sub": "bob", "preferred_username": "bob", "email": "bob@example.com", "name": "Bob"}'