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/interactive/components/custom-editor.ts

@@ -1,5 +1,6 @@
 import {
 	Editor,
+	isAltEnter,
 	isCtrlC,
 	isCtrlD,
 	isCtrlG,
@@ -28,8 +29,14 @@ export class CustomEditor extends Editor {
 	public onCtrlT?: () => void;
 	public onCtrlG?: () => void;
 	public onCtrlZ?: () => void;
+	public onAltEnter?: () => void;
 
 	handleInput(data: string): void {
+		// Intercept Alt+Enter for follow-up messages
+		if (isAltEnter(data) && this.onAltEnter) {
+			this.onAltEnter();
+			return;
+		}
 		// Intercept Ctrl+G for external editor
 		if (isCtrlG(data) && this.onCtrlG) {
 			this.onCtrlG();