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/coding-agent/src/modes/rpc/rpc-client.ts

@@ -173,10 +173,17 @@ export class RpcClient {
 	}
 
 	/**
-	 * Queue a message while agent is streaming.
+	 * Queue a steering message to interrupt the agent mid-run.
 	 */
-	async queueMessage(message: string): Promise<void> {
-		await this.send({ type: "queue_message", message });
+	async steer(message: string): Promise<void> {
+		await this.send({ type: "steer", message });
+	}
+
+	/**
+	 * Queue a follow-up message to be processed after the agent finishes.
+	 */
+	async followUp(message: string): Promise<void> {
+		await this.send({ type: "follow_up", message });
 	}
 
 	/**
@@ -248,10 +255,17 @@ export class RpcClient {
 	}
 
 	/**
-	 * Set queue mode.
+	 * Set steering mode.
 	 */
-	async setQueueMode(mode: "all" | "one-at-a-time"): Promise<void> {
-		await this.send({ type: "set_queue_mode", mode });
+	async setSteeringMode(mode: "all" | "one-at-a-time"): Promise<void> {
+		await this.send({ type: "set_steering_mode", mode });
+	}
+
+	/**
+	 * Set follow-up mode.
+	 */
+	async setFollowUpMode(mode: "all" | "one-at-a-time"): Promise<void> {
+		await this.send({ type: "set_follow_up_mode", mode });
 	}
 
 	/**