Rename /branch command to /fork

- RPC: branch -> fork, get_branch_messages -> get_fork_messages
- SDK: branch() -> fork(), getBranchMessages() -> getForkMessages()
- AgentSession: branch() -> fork(), getUserMessagesForBranching() -> getUserMessagesForForking()
- Extension events: session_before_branch -> session_before_fork, session_branch -> session_fork
- Settings: doubleEscapeAction 'branch' -> 'fork'

fixes #641

packages/coding-agent/src/core/extensions/index.ts

@@ -9,8 +9,8 @@ export {
 	loadExtensions,
 } from "./loader.js";
 export type {
-	BranchHandler,
 	ExtensionErrorListener,
+	ForkHandler,
 	NavigateTreeHandler,
 	NewSessionHandler,
 	ShutdownHandler,
@@ -75,17 +75,17 @@ export type {
 	RegisteredTool,
 	SendMessageHandler,
 	SendUserMessageHandler,
-	SessionBeforeBranchEvent,
-	SessionBeforeBranchResult,
 	SessionBeforeCompactEvent,
 	SessionBeforeCompactResult,
+	SessionBeforeForkEvent,
+	SessionBeforeForkResult,
 	SessionBeforeSwitchEvent,
 	SessionBeforeSwitchResult,
 	SessionBeforeTreeEvent,
 	SessionBeforeTreeResult,
-	SessionBranchEvent,
 	SessionCompactEvent,
 	SessionEvent,
+	SessionForkEvent,
 	SessionShutdownEvent,
 	// Events - Session
 	SessionStartEvent,