feat: install.sh + auto-update checker for CLI

- tools/install.sh: standalone installer/upgrader, curl-pipe safe
  (main() wrapper, process.argv instead of stdin, mkdir -p prefix)
- packages/mosaic/src/runtime/update-checker.ts: version check module
  with 1h cache at ~/.cache/mosaic/update-check.json
- CLI startup: non-blocking background update check on every invocation
- 'mosaic update' command: explicit check + install (--check for CI)
- session-start.sh: warns agents when CLI is outdated
- Proper semver comparison including pre-release precedence
- eslint: allow __tests__ in packages/mosaic for projectService

eslint.config.mjs

@@ -27,6 +27,7 @@ export default tseslint.config(
             'apps/web/e2e/*.ts',
             'apps/web/e2e/helpers/*.ts',
             'apps/web/playwright.config.ts',
+            'packages/mosaic/__tests__/*.ts',
           ],
         },
       },