fix(model-suggestion-retry): release reservation on async error path

The promptWithModelSuggestionRetry async variant did not release the
post-dispatch reservation when the wrapped promptAsync threw. Callers
that immediately retry (such as sendSyncPrompt error toast paths) hit
the gate as reserved and surfaced 'promptAsync skipped by gate: reserved'
instead of the underlying error.

Mirrors the existing sync variant fix from ff1b15d53.

Closes regression introduced by BLOCKER-2 hardening

src/shared/model-suggestion-retry.ts

@@ -123,6 +123,7 @@ export async function promptWithModelSuggestionRetry(
     if (timeoutContext.wasTimedOut()) {
       throw new Error(`promptAsync timed out after ${timeoutMs}ms`)
     }
+    releasePromptAsyncReservation(args.path.id, "model-suggestion-retry")
     throw error
   } finally {
     timeoutContext.cleanup()