refactor: Add explicit return types and improve type safety

- Added explicit return types to all public command functions
- Added type assertion guards for validateAgent and validateCloud
- Added explicit types to Promise callbacks (code parameter)
- Added explicit type to mapToSelectOptions return value
- Improved type narrowing in getImplementedClouds filter
- Added explicit encoding parameter to writeCache

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

cli/src/commands.ts

@@ -13,6 +13,7 @@ import {
   type Manifest,
 } from "./manifest.js";
 import { VERSION } from "./version.js";
+import { validateIdentifier, validateScriptContent } from "./security.js";
 
 // ── Helpers ────────────────────────────────────────────────────────────────────