feat: add in-browser dial pad with Twilio Voice SDK

- New DialPad component on Patient Connection page: clickable keypad,
  call/hangup/mute buttons, duration timer, keyboard input support
- Backend: POST /api/twilio/voice-token issues Access Token for browser
  Device; POST /api/twilio/webhook/voice-browser is the TwiML webhook
  Twilio calls to bridge the browser to the patient's phone
- TwiML App SID field added to Twilio Settings (stored in templates JSON)
- README: one-time Twilio Console setup instructions for the dial pad

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/Frontend/package.json

@@ -48,6 +48,7 @@
     "@tailwindcss/vite": "^4.1.6",
     "@tanstack/react-query": "^5.60.5",
     "@tanstack/react-table": "^8.21.3",
+    "@twilio/voice-sdk": "^2.18.3",
     "autoprefixer": "^10.4.20",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",