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>

src/utils.ts

@@ -0,0 +1,18 @@
+import fs from 'fs';
+import path from 'path';
+
+export function loadJson<T>(filePath: string, defaultValue: T): T {
+  try {
+    if (fs.existsSync(filePath)) {
+      return JSON.parse(fs.readFileSync(filePath, 'utf-8'));
+    }
+  } catch {
+    // Return default on error
+  }
+  return defaultValue;
+}
+
+export function saveJson(filePath: string, data: unknown): void {
+  fs.mkdirSync(path.dirname(filePath), { recursive: true });
+  fs.writeFileSync(filePath, JSON.stringify(data, null, 2));
+}