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>

CLAUDE.md

@@ -475,3 +475,25 @@ Related Repositories
 ---
 
 Mosaic Stack v0.0.x — Building the future of personal assistants.
+
+## Campsite Rule (MANDATORY)
+
+If you modify a line containing a policy violation, you MUST either:
+
+1. **Fix the violation properly** in the same change, OR
+2. **Flag it as a deferred item** with documented rationale
+
+**"It was already there" is NEVER an acceptable justification** for perpetuating a violation in code you touched. Touching it makes it yours.
+
+Examples of violations you must fix when you touch the line:
+
+- `as unknown as Type` double assertions — use type guards instead
+- `any` types — narrow to `unknown` with validation or define a proper interface
+- Missing error handling — add it if you're modifying the surrounding code
+- Suppressed linting rules (`// eslint-disable`) — fix the underlying issue
+
+If the proper fix is too large for the current scope, you MUST:
+
+- Create a TODO comment with issue reference: `// TODO(#123): Replace double assertion with type guard`
+- Document the deferral in your PR/commit description
+- Never silently carry the violation forward