fix(prepare): Detect pending remote release branches

[BYK]

Summary

• inspect every effective push destination before release preparation starts
• stop pending releases before GitHub outputs, prompts, or dry-run worktrees
• push with an exact refspec and an expected-absent lease to close the preflight race
• keep --no-push guidance race-safe
• add end-to-end coverage for push URLs, query failures, races, successful pushes, and disabled pushes

Testing

• pnpm test src/__tests__/prepare-dry-run.e2e.test.ts --printConsoleTrace (14 passed)
• pnpm test --printConsoleTrace (1,212 passed, 1 skipped)
• pnpm typecheck
• pnpm lint (0 errors, 7 existing warnings)
• pnpm format:check
• pnpm build

Closes #882