Add GetRigs command, rig_id routing fields, and RigEntry type:
- ClientCommand::GetRigs (intercepted in listener before rig_task)
- rig_id: Option<String> on ClientEnvelope (absent = first rig)
- rig_id: Option<String> and rigs: Option<Vec<RigEntry>> on ClientResponse
- RigEntry { rig_id, state } for GetRigs aggregated response
- Sentinel unreachable!() arm for GetRigs in client_command_to_rig()
- MR-09 codec tests: rig_id parsing, GetRigs round-trip, serde omit-when-None
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>
sjg
bb3464e32f