Add guestbook with WebAuthn admin and SQLite

Introduce server-rendered guestbook and moderation portal.
Persist data in SQLite (better-sqlite3); add WebAuthn YubiKey
admin auth, rate-limiting, spam heuristics, and sanitization.
Switch Docker image to run Node/standalone Astro (remove nginx),
update docker-compose, Dockerfile, astro.config, and package.json.
Add .env.example, docs/guestbook.md, gitignore updates, layouts,
API routes, and supporting lib/components/pages for the feature.

docker-compose.yml

@@ -3,7 +3,19 @@ services:
     build: .
     container_name: cozy-den
     ports:
-      - "3000:80"
+      - "3000:3000"
     restart: unless-stopped
     environment:
       - NODE_ENV=production
+      - HOST=0.0.0.0
+      - PORT=3000
+      - DB_PATH=/data/guestbook.db
+      - SECRET_KEY=${SECRET_KEY}
+      - WEBAUTHN_RP_ID=${WEBAUTHN_RP_ID:-hiddenden.cafe}
+      - WEBAUTHN_RP_NAME=${WEBAUTHN_RP_NAME:-Cozy Den}
+      - WEBAUTHN_ORIGIN=${WEBAUTHN_ORIGIN:-https://hiddenden.cafe}
+    volumes:
+      - guestbook_data:/data
+
+volumes:
+  guestbook_data: