Recover stale community entries

[baxen]

Why

Changing identities can leave Desktop with a stale local community entry and a pending onboarding transaction. When the correct saved community uses the requested relay URL, the duplicate-relay guard currently leaves the user with no in-app recovery path.

What

• Offer an explicit local-only replacement when another saved community already uses the requested relay
• Remove the stale entry and scoped caches, then activate the existing saved community
• Retarget the pending onboarding transaction so retry and cancel cannot reference the removed entry

Risk Assessment

Low — the repair requires confirmation and only changes local Desktop state. It does not mutate either relay or the persisted Nostr identity.

Verification

• pnpm typecheck
• pnpm check
• Focused community/onboarding tests: 19 passed
• Full Desktop tests: 3,174 passed
• Pre-push Tauri Rust suite: 1,472 passed; 3 existing Codex adapter probe tests failed for the same unrelated environment issue reproduced on prior branches

Generated with Codex

[baxen]

Superseded by the foundational state-model approach agreed in the Buzz design thread: make community selection nullable, provide an always-renderable Community Home, and separate saved configuration, current-session usability, and onboarding operations. The stale-entry replacement/transaction-retargeting mechanism in this PR couples recovery to the wrong event. We will preserve the original wedge as a transition regression and reuse the scoped cache-cleanup behavior in the replacement implementation.