chore: upgrade Node.js runtime to v24 across codebase

- Update .woodpecker/codex-review.yml: node:22-slim → node:24-slim
- Update packages/cli-tools engines: >=18 → >=24.0.0
- Update README.md, CONTRIBUTING.md, prerequisites docs to reference Node 24+
- Rename eslint.config.js → eslint.config.mjs to eliminate Node 24
  MODULE_TYPELESS_PACKAGE_JSON warnings (ESM detection overhead)
- Add .nvmrc targeting Node 24
- Fix pre-existing no-unsafe-return lint error in matrix-room.service.ts
- Add Campsite Rule to CLAUDE.md
- Regenerate Prisma client for Node 24 compatibility

All Dockerfiles and main CI pipelines already used node:24. This commit
aligns the remaining stragglers (codex-review CI, cli-tools engines,
documentation) and resolves Node 24 ESM module detection warnings.

Quality gates: lint ✅ typecheck ✅ tests ✅ (6 pre-existing API failures)

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

apps/api/src/bridge/matrix/matrix-room.service.ts

@@ -93,7 +93,10 @@ export class MatrixRoomService {
       select: { matrixRoomId: true },
     });
 
-    return workspace?.matrixRoomId ?? null;
+    if (!workspace) {
+      return null;
+    }
+    return workspace.matrixRoomId ?? null;
   }
 
   /**