build(layer2+3): propagate .build/+dist/ to Docker/Electron/CI; codify light deploy; docs

Layer 3: Dockerfile COPY .next/standalone -> .build/next/standalone (+cache mount);
electron stage -> .build/electron-standalone + extraResources; CI asserts dist/server.js;
eslint ignores .build/**+dist/**. Layer 2: deploy-vps-* skills use build:release + rsync(dist)
-> remote app/ + pm2 restart + BUILD_SHA verify (drop npm-i-g/legacy-peer-deps/manual-wreq).
Docs (RELEASE_CHECKLIST/CONTRIBUTING/AGENTS/CHANGELOG) describe src/+.build/+dist/ layout.
Verified: docker build exit 0 + health 200; electron stage OK; no stale build-output refs.

.github/workflows/ci.yml

@@ -159,7 +159,11 @@ jobs:
           cache: npm
       - run: npm ci
       - run: npm run check:node-runtime
+      # build:cli runs a clean build into .build/next and assembles dist/
+      # For release builds prefer: npm run build:release (clean rebuild + HEAD sentinel)
       - run: npm run build:cli
+      - name: Assert dist/server.js exists
+        run: test -f dist/server.js || (echo "dist/server.js missing — build:cli did not assemble correctly" && exit 1)
       - run: npm run check:pack-artifact
 
   electron-package-smoke: