fix(cli): always dispose instance on error to prevent hanging; add friendly ProviderModelNotFoundError/InitError messages\n\n- Wrap bootstrap callback in try/finally to guarantee Instance.dispose()\n- Format provider/model errors into actionable guidance (opencode models, config)\n\nRepro: running `opencode run --model typo/claude-haiku-4-5` prints stack and hangs until SIGINT due to lingering watchers.\nFix: disposing Instance tears down watchers/subscriptions, allowing process to exit.\n\nNotes: Prior attempt (#3083) explicitly exited; this approach addresses root cause without forcing exit and improves UX for common misconfigurations.