Refactor: delete dead code, extract utils, rename files for clarity

- Delete scheduler-mcp.ts (285 lines of dead code, unused)
- Extract loadJson/saveJson to utils.ts (generic utilities)
- Rename auth.ts → whatsapp-auth.ts (more specific)
- Rename scheduler.ts → task-scheduler.ts (more specific)
- Update all references in docs and imports

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -8,7 +8,7 @@
     "build": "tsc",
     "start": "node dist/index.js",
     "dev": "tsx src/index.ts",
-    "auth": "tsx src/auth.ts",
+    "auth": "tsx src/whatsapp-auth.ts",
     "lint": "eslint src/",
     "typecheck": "tsc --noEmit"
   },