feat: add rb ffprobe command

[a-essawy]

Summary

Adds rb ffprobe [flags] <url-or-file> for probing media metadata in the cloud, mirroring rb ffmpeg's structure (auth flow, StepRenderer spinner, error handling, data-only output rendering) but simplified for a fast, data-only job: it uses client.jobs.wait() directly instead of the WebSocket/machine-context ceremony rb ffmpeg needs for longer renders.

• Positional arg accepts a URL or a local file path (local files are auto-uploaded first via the existing upload lib, same as rb ffmpeg).
• Flags: --keyframes, --raw, --json, --quiet, --no-wait, --timeout N (clamped to 900s).
• Default output: result.output.data.summary pretty-printed to stdout (pipeable to jq). --raw prints the full output.data (format/streams/chapters). --json prints the full job result.
• Registered in src/registry.ts under the CORE group.
• No SDK bump needed — jobs.create/jobs.wait are generic over the string job type in the currently-published @rendobar/sdk.

Notes

• The ffprobe job type is not live in prod yet — this command will error (job type not found) until rendobar/rendobar#349 ships. Do not merge this before that lands.
• Opened as a draft for that reason.

Test plan

• pnpm test — 149 tests pass (includes new ffprobe-command.test.ts covering flag parsing, url-vs-local detection, timeout clamping, and the local-upload reuse path — no network calls)
• pnpm typecheck — clean
• pnpm build — compiles; smoke-tested rb ffprobe (empty-args help), rb ffprobe --help, and the unauthenticated error path locally
• Live job submission (blocked until the backend ffprobe job type ships)