feat(09-05): ProfileChannelsSection (Teams + ntfy + QR code) + qrcode.react install

- Create ProfileChannelsSection.tsx with Teams + ntfy sub-sections
- Teams: URL input, inline 400 error (teamsError), save/clear buttons, inline test result
- ntfy: mint-on-first-save (State A → State B), QR code via QRCodeSVG, subscribe link
- ntfy: advanced disclosure with custom topic input + inline 400 error (customTopicError)
- ntfy: test-now and remove buttons
- Install qrcode.react ^4.2.0 (node_modules + package.json + package-lock.json updated)
- Delete ProfileChannelsSectionPlaceholder.tsx (replaced by real component)
- Update app/mobile/profile/page.tsx import to ProfileChannelsSection (not Placeholder)

package.json

@@ -46,6 +46,7 @@
     "node-cron": "^4.2.1",
     "nodemailer": "^7.0.12",
     "pg": "^8.11.0",
+    "qrcode.react": "^4.2.0",
     "radix-ui": "^1.4.3",
     "react": "19.2.3",
     "react-day-picker": "^9.13.0",