feat: git SHA version badge in admin, fix finanzplan caching, drop gitea remote

- AdminShell: shows NEXT_PUBLIC_GIT_SHA in sidebar footer
- Dockerfile + build-pitch-deck.yml: pass --build-arg GIT_SHA at build time
- FinanzplanSlide: fetch with cache:no-store to always show current DB values
- finanzplan routes: Cache-Control: no-store to prevent CDN/proxy staling
- CLAUDE.md: remove dead gitea remote (only origin exists)

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

pitch-deck/next.config.js

@@ -1,6 +1,9 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {
   output: 'standalone',
+  env: {
+    NEXT_PUBLIC_GIT_SHA: process.env.GIT_SHA || 'dev',
+  },
   reactStrictMode: true,
   typescript: {
     ignoreBuildErrors: true,