fix(desktop): allow removing a community from this device without its relay

[eran-rom]

Summary

A saved community can become impossible to remove when its relay goes down or returns HTTP 404, because Leave community requires relay communication before local cleanup.

After Leave community fails because the relay is unavailable, offer a confirmed Remove from this device fallback beneath the error. It removes the saved connection without contacting the relay, keeps the user's identity, and switches to another community or returns to community discovery. The confirmation explains that server membership is unchanged and the community itself is not deleted.

Recognize network failures, disconnected WebSockets, leave-request timeouts, and HTTP 404/410/5xx responses. Relay permission errors and owner restrictions do not expose this fallback.

Reuse the existing local cleanup and navigation flow. Leave community continues to require relay acceptance.

Related issue

Fixes #7754.

Related: #7049, #7097 and #3621. This covers local removal when the relay is unavailable, including the HTTP 404 case; #7097 addresses revoked membership with a reachable relay.

Testing

• Full desktop unit suite: 6,510 passed, including availability classification and a WebSocket failure after the membership check succeeds.
• Targeted Playwright tests with the mocked Tauri bridge: 5 passed. Cover HTTP 404, an unreachable relay, permission rejection, cancellation, saved-state persistence, identity preservation, fallback navigation, and ordinary leaving.
• Full desktop lint checks and production build passed. The E2E build, file-size checks, and git diff --check also passed.
• Regression checks failed against the original behavior before the fix.
• No live relay or installed-app testing.

Full just ci passed, using the repository-required nextest 0.9.136 from a temporary tools directory. This includes repository lint/policy checks, Rust/native/desktop/mobile tests, and desktop/web builds.

Screenshots

Captured with the mocked Tauri bridge; no live relay or installed app was used.

Before: the failed leave has no local-removal action.

After: the availability error exposes the local-removal fallback.

Confirmation explains the effect on the device and server membership.

[github-actions]

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