fix: Add missing __init__.py to routers package

The routers package was missing its __init__.py file, causing ModuleNotFoundError
when trying to import whatsapp_router. This prevented the application from starting
and caused App Runner health check failures.

Resolves deployment issue from PR #192 where the router was moved from
src/ansari/app/main_whatsapp.py to src/ansari/routers/whatsapp_router.py
but the package initialization file was not added.

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

Author: OdyAsh