feat(ui): record the SDK load outcome in the launch diagnostic

The diagnostic showed only sdk: yes/no (window.Telegram presence), not why the
SDK was absent. Capture how the dynamic telegram-web-app.js load resolved —
present / loaded / no-webapp / error / timeout — and surface it as
"sdk-load: <outcome>". error/timeout pinpoint a blocked or hanging telegram.org
(the prime suspect for an empty launch); no-webapp a loaded-but-broken script.

loadTelegramSDK records the outcome (telegramSdkOutcome); collectTelegramDiag
carries it into the screen. Unit tests cover each outcome; the blocked-script
e2e now asserts sdk-load: error.

ui/src/screens/TelegramLaunchError.svelte

@@ -17,6 +17,7 @@
   const report = $derived(
     diag
       ? [
+          `sdk-load: ${diag.sdkLoad}`,
           `sdk: ${diag.hasSDK ? 'yes' : 'no'}   webapp: ${diag.hasWebApp ? 'yes' : 'no'}`,
           `tg-platform: ${diag.platform || '—'}   tg-version: ${diag.version || '—'}`,
           `initData: ${diag.initDataLen > 0 ? diag.initDataLen : 'empty'}   tgdata-in-url: ${diag.hashHadTgData ? 'yes' : 'no'}`,