feat(coding-agent): complete steer()/followUp() migration

- Update settings-manager with steeringMode/followUpMode (migrates old queueMode)
- Update sdk.ts to use new mode options
- Update settings-selector UI to show both modes
- Add Alt+Enter keybind for follow-up messages
- Update RPC API: steer/follow_up commands, set_steering_mode/set_follow_up_mode
- Update rpc-client with new methods
- Delete dead code: queue-mode-selector.ts
- Update tests for new API
- Update mom/context.ts stubs
- Update web-ui example

packages/mom/src/context.ts

@@ -495,11 +495,19 @@ export class MomSettingsManager {
 	}
 
 	// Compatibility methods for AgentSession
-	getQueueMode(): "all" | "one-at-a-time" {
+	getSteeringMode(): "all" | "one-at-a-time" {
 		return "one-at-a-time"; // Mom processes one message at a time
 	}
 
-	setQueueMode(_mode: "all" | "one-at-a-time"): void {
+	setSteeringMode(_mode: "all" | "one-at-a-time"): void {
+		// No-op for mom
+	}
+
+	getFollowUpMode(): "all" | "one-at-a-time" {
+		return "one-at-a-time"; // Mom processes one message at a time
+	}
+
+	setFollowUpMode(_mode: "all" | "one-at-a-time"): void {
 		// No-op for mom
 	}