feat(composer): replicate WorkBuddy branch label and context usage (TODO 21)

src/preload/index.ts

@@ -99,6 +99,9 @@ const api: YCodeApi = {
       return () => ipcRenderer.removeListener('settings:changed', handler)
     }
   },
+  git: {
+    branch: (sessionId) => ipcRenderer.invoke('git:branch', sessionId)
+  },
   config: {
     get: () => ipcRenderer.invoke('config:get'),
     update: (patch: ConfigPatchLike) => ipcRenderer.invoke('config:update', patch)