fix: pin matrix-js-sdk to a working commit, use our own Element Call fork

The floating github:matrix-org/matrix-js-sdk#develop reference was
resolved to a stale commit missing src/oidc/authorize.ts (breaking the
webpack build). Investigated moving to the current develop HEAD instead
(191908da) - turned out to be worse, not better: that commit renamed the
entire src/oidc/ module to src/oauth/ with a materially different API
(generateOidcAuthorizationUrl/completeAuthorizationCodeGrant/OidcError
don't exist under those names anymore). Rather than porting our OIDC
login code to the new API sight-unseen, pinned to d19cb751 - the last
develop commit before that rename, verified to have both the file at
the expected path and the exact exports apps/web imports.

Also switched the Element Call embedded widget dependency from
upstream's @element-hq/element-call-embedded to our own published fork
(@sorb/threadnet-call-embedded@0.19.2-threadnet.5) - a full rebuild was
otherwise silently bundling the unmodified upstream widget, discarding
every Element Call customization (Video-tab quality settings, German
translations, codec list fix).

apps/web/package.json

@@ -81,7 +81,7 @@
         "lodash": "npm:lodash-es@4.18.1",
         "maplibre-gl": "^5.0.0",
         "matrix-encrypt-attachment": "^1.0.3",
-        "matrix-js-sdk": "github:matrix-org/matrix-js-sdk#develop",
+        "matrix-js-sdk": "github:matrix-org/matrix-js-sdk#d19cb751da8bbdc75c19db751fff25f21761d23a",
         "matrix-widget-api": "^1.16.1",
         "memoize-one": "^6.0.0",
         "mime": "^4.0.4",
@@ -125,7 +125,7 @@
         "@babel/preset-react": "^7.12.10",
         "@babel/preset-typescript": "^7.12.7",
         "@casualbot/jest-sonar-reporter": "2.7.0",
-        "@element-hq/element-call-embedded": "0.19.2",
+        "@sorb/threadnet-call-embedded": "0.19.2-threadnet.5",
         "@element-hq/element-web-playwright-common": "workspace:*",
         "@fetch-mock/jest": "^0.2.20",
         "@jest/globals": "^30.2.0",