Auto-Update über Gitea einrichten + Web-Editor + Sync-Verbesserungen

- Thunderbird Auto-Update: update_url im Manifest, updates.json, release.sh
- .xpi neu gebaut (mit update_url, ohne defaults.local.json/Token)
- README + CLAUDE.md: Auto-Update-Doku, Repo muss public bleiben
- web-editor/ (Node/Docker WYSIWYG-Editor) hinzugefügt
- gitea-sync.js + templates_options: bestehende Anpassungen

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web-editor/Dockerfile

@@ -0,0 +1,20 @@
+FROM node:20-alpine
+
+WORKDIR /app
+
+# Install dependencies first for better layer caching.
+COPY package.json ./
+RUN npm install --omit=dev
+
+# App source.
+COPY server.js ./
+COPY public ./public
+
+ENV PORT=3000
+EXPOSE 3000
+
+# Lightweight container healthcheck against the API.
+HEALTHCHECK --interval=30s --timeout=5s --start-period=5s --retries=3 \
+  CMD wget -qO- http://localhost:3000/api/config > /dev/null || exit 1
+
+CMD ["node", "server.js"]