feat(host-agent): Phase 1b RCON — WebRCON (rust) + Source RCON (conan/soulmask)

rcon func on the instance command channel: WebSocket JSON WebRCON with
Identifier correlation (skips chat/log noise frames) and full Valve
Source RCON over TCP (auth, exec, multi-packet reassembly via empty
probe, 1MiB cap). Protocol inferred from game, explicit kind override
in [instance.rcon]. Always 127.0.0.1 — agent is co-located.

Hardening from review: WebRCON password never interpolated into error
contexts/logs (redacted URL); probe-tolerant termination — a quiet
period after received data ends the response for servers that don't
echo the probe (Soulmask conformance unverified), so data is never
discarded on probe timeout.

13/13 tests green incl. mock Source-RCON server (auth/multi-packet/
errors) and mock WebRCON server (noise-frame skipping).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

corrosion-host-agent/tests/supervisor.rs

@@ -19,6 +19,7 @@ fn managed_instance(executable: &str, args: &[&str]) -> InstanceConfig {
         executable: Some(PathBuf::from(executable)),
         args: args.iter().map(|s| s.to_string()).collect(),
         working_dir: None,
+        rcon: None,
     }
 }