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/modes/print-mode.ts

@@ -78,8 +78,8 @@ export async function runPrintMode(session: AgentSession, options: PrintModeOpti
 					}
 					return { cancelled: !success };
 				},
-				branch: async (entryId) => {
-					const result = await session.branch(entryId);
+				fork: async (entryId) => {
+					const result = await session.fork(entryId);
 					return { cancelled: result.cancelled };
 				},
 				navigateTree: async (targetId, options) => {