feat: migrate SMS/voice to Telnyx (TeXML), keep browser dial pad on Twilio

Twilio now handles only the in-browser dial pad (Access Token + browser-Device
outbound TwiML); Telnyx takes over SMS, inbound voicemail, the AI voice
conversation loop, and staff-triggered outbound calls via TeXML. Adds
TelnyxSettings model, Communication.provider discriminator, new comms/routes
modules, and a real Telnyx Settings page.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

package-lock.json

@@ -59,6 +59,7 @@
         "pdfkit": "^0.17.2",
         "sharp": "^0.35.3",
         "socket.io": "^4.8.1",
+        "telnyx": "^7.20.0",
         "twilio": "^6.0.0",
         "ws": "^8.18.0",
         "zod": "^3.24.2",
@@ -14003,6 +14004,20 @@
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       "license": "ISC"
     },
+    "node_modules/telnyx": {
+      "version": "7.20.0",
+      "resolved": "https://registry.npmjs.org/telnyx/-/telnyx-7.20.0.tgz",
+      "integrity": "sha512-Y+M9h8I9cvd/Zv/RzgrWnQX22VJx8+oClwGtsxvwr3lfkA+Gl0XutwuDmKhuIzTcyrpkf/qCdC2kjPYARqXrqw==",
+      "license": "MIT",
+      "peerDependencies": {
+        "ws": "^8.18.0"
+      },
+      "peerDependenciesMeta": {
+        "ws": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/text-decoder": {
       "version": "1.2.7",
       "resolved": "https://registry.npmjs.org/text-decoder/-/text-decoder-1.2.7.tgz",