refactor: consolidate MCP factory, add non-TTY support, auto-detect transcript watchers

- Phase 1: Replace 5 duplicate MCP installers with config-driven factory, extract
  shared context-injection and json-utils utilities, fix process.execPath usage
- Phase 2: Add non-TTY fallback for @clack/prompts to prevent ENOENT in CI/Docker
- Phase 3: Wire GeminiCliHooksInstaller through hook command framework with adapter
- Phase 4: Auto-start transcript watchers on worker boot when config exists

Net -107 lines via DRY consolidation of duplicated installer logic.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/npx-cli/utils/paths.ts

@@ -137,14 +137,11 @@ export function ensureDirectoryExists(directoryPath: string): void {
   }
 }
 
-export function readJsonFileSafe(filepath: string): any {
-  if (!existsSync(filepath)) return {};
-  try {
-    return JSON.parse(readFileSync(filepath, 'utf-8'));
-  } catch {
-    return {};
-  }
-}
+/**
+ * @deprecated Use `readJsonSafe` from `../../utils/json-utils.js` instead.
+ * Kept as re-export for backward compatibility.
+ */
+export { readJsonSafe } from '../../utils/json-utils.js';
 
 export function writeJsonFileAtomic(filepath: string, data: any): void {
   ensureDirectoryExists(dirname(filepath));