Fall back to publishing on a remote SFU if possible

Port of edf1feae from johannes/rtc-remote-publish onto the SDK split,
where
the MatrixRTC logic lives in sdk/ rather than src/state/CallViewModel/.

Where the original lands:

- getLocalTransport's remote fallback: the LiveKit backend's new
  findRemotePublishTransport (sdk/src/media-backend/livekit/
  RemotePublishTransport.ts), which tries the candidates from the
  js-sdk's
  getRemoteLivekitPublishCandidates oldest first and keeps the first
  whose
  homeserver issues a token with the publish grant.
  discoverLocalTransport
  asks the backend for it after the host's fallback, with a snapshot of
  the
  session's memberships from RTCParticipation, and throws
  MatrixRTCTransportMissingError where that finds nothing too. Transport
  discovery stays backend neutral: the MSC4195 token check is the
  backend's.
- LocalMember's "no delegation on a remote SFU" and the custom
  transport's
  server_name: LivekitBackend.prepareLocalTransport locates the
  transport on
  the homeserver it names (serverNameOfTransport) and skips the
  delegation
  probe where that is not our own.
- SessionBehaviors' membership.getTransportServerName: the same helper
  in
  LivekitBackend.mediaFor.
- decodeSFUJWTPayload, SFUJWTPayload.video.canPublish and the exported
  isCsApiUnavailable: sdk/src/media-backend/livekit/auth/.
- DeveloperSettingsTab, the widget capabilities, the locale string and
  the
  js-sdk pin (9405287c, 44.0.0): applied as is. The error boundary
  snapshots follow the string.

Tests: the LocalTransport cases go to RemotePublishTransport.test.ts and
LocalTransport.test.ts, the LocalMember remote case and the
SessionBehaviors
server-name case to LivekitBackend.test.ts, plus the memberships
snapshot in
RTCParticipation.test.ts.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

pnpm-lock.yaml

@@ -191,8 +191,8 @@ importers:
         specifier: ^1.9.1
         version: 1.9.2
       matrix-js-sdk:
-        specifier: github:matrix-org/matrix-js-sdk#develop
-        version: https://codeload.github.com/matrix-org/matrix-js-sdk/tar.gz/4df2f2bfb5826c25f05d9535a8556acecaf2e570
+        specifier: github:matrix-org/matrix-js-sdk#9405287c22797e9d69acd366c47bf412fa4384c8
+        version: https://codeload.github.com/matrix-org/matrix-js-sdk/tar.gz/9405287c22797e9d69acd366c47bf412fa4384c8
       matrix-widget-api:
         specifier: ^1.18.0
         version: 1.20.0
@@ -4673,9 +4673,9 @@ packages:
   matrix-events-sdk@0.0.1:
     resolution: {integrity: sha512-1QEOsXO+bhyCroIe2/A5OwaxHvBm7EsSQ46DEDn8RBIfQwN5HWBpFvyWWR4QY0KHPPnnJdI99wgRiAl7Ad5qaA==}
 
-  matrix-js-sdk@https://codeload.github.com/matrix-org/matrix-js-sdk/tar.gz/4df2f2bfb5826c25f05d9535a8556acecaf2e570:
-    resolution: {gitHosted: true, integrity: sha512-b1o6ywaPY9jakj+3GIgx3samM9AbqohzPQ5nZKbyOGYB16IHQtNMyjEo/PY0fW/s0uwBVApEHNb/MMtN40c/rQ==, tarball: https://codeload.github.com/matrix-org/matrix-js-sdk/tar.gz/4df2f2bfb5826c25f05d9535a8556acecaf2e570}
-    version: 43.0.0
+  matrix-js-sdk@https://codeload.github.com/matrix-org/matrix-js-sdk/tar.gz/9405287c22797e9d69acd366c47bf412fa4384c8:
+    resolution: {gitHosted: true, integrity: sha512-pYk38ggTEdM0WWXLDiFoKmyRn3wo3o8m1ge0iCtxjBmgAW5qoQ2Ifd8oHVy+gu6PQe/CfLuKPXEXH8hff9C8GA==, tarball: https://codeload.github.com/matrix-org/matrix-js-sdk/tar.gz/9405287c22797e9d69acd366c47bf412fa4384c8}
+    version: 44.0.0
     engines: {node: '>=22.0.0'}
 
   matrix-widget-api@1.20.0:
@@ -10227,7 +10227,7 @@ snapshots:
 
   matrix-events-sdk@0.0.1: {}
 
-  matrix-js-sdk@https://codeload.github.com/matrix-org/matrix-js-sdk/tar.gz/4df2f2bfb5826c25f05d9535a8556acecaf2e570:
+  matrix-js-sdk@https://codeload.github.com/matrix-org/matrix-js-sdk/tar.gz/9405287c22797e9d69acd366c47bf412fa4384c8:
     dependencies:
       '@babel/runtime': 8.0.0
       '@matrix-org/matrix-sdk-crypto-wasm': 18.9.0