fix: harden update pipeline and restore a clean production build

- update-Nitrov3.sh: build CMS into .next-staging and swap atomically so a
  failed build never takes the live site down; auto-merge new variables
  from .env.example; validate env for duplicates/broken lines; restart the
  emulator/CMS only when rebuilt or unhealthy; fix step renumbering
- next.config.ts: support NEXT_DIST_DIR for staged production builds
- fix all TS errors (unused imports, missing tryDownloadCandidates helper)
  so tsc and the production build pass clean
- add Dockerfile/.dockerignore and switch docker-compose to a CMS container
- include prevailing UI/refactor changes (SurfaceCard, ticketing, tsconfig)

.dockerignore

@@ -0,0 +1,14 @@
+.git
+.gitignore
+.next
+node_modules
+coverage
+storage
+prod.log
+update.log
+.pm2
+.env
+*.tsbuildinfo
+# ~3GB client assets; mounted as a volume at runtime (see docker-compose.yml)
+public/nitro-assets
+public/swf