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/Backend/src/storage/twilio-storage.ts

@@ -5,6 +5,7 @@ export type TwilioSettingsData = {
   authToken: string;
   phoneNumber: string;
   greetingMessage?: string | null;
+  twimlAppSid?: string | null;
 };
 
 export type CommunicationCreateData = {
@@ -24,10 +25,18 @@ export const twilioStorage = {
   },
 
   async upsertTwilioSettings(userId: number, data: TwilioSettingsData) {
+    const { twimlAppSid, ...rest } = data;
+    const existing = await db.twilioSettings.findUnique({ where: { userId } });
+    const existingTemplates = (existing?.templates as Record<string, string>) || {};
+    const templates: Record<string, string> = { ...existingTemplates };
+    if (twimlAppSid !== undefined) {
+      if (twimlAppSid) templates["_twiml_app_sid"] = twimlAppSid;
+      else delete templates["_twiml_app_sid"];
+    }
     return db.twilioSettings.upsert({
       where: { userId },
-      update: data,
-      create: { userId, ...data },
+      update: { ...rest, templates },
+      create: { userId, ...rest, templates },
     });
   },