feat(create-review): load repository branches and suggest local branch

Add a backend command to enumerate a repository's branches and default
branch for configured integrations, and expose it to the UI. The create
review dialog now fetches branches, shows loading and error states, and
uses searchable SelectMenu controls for repositories and branches. If a
local repository path is available the dialog will try to match remotes
and preselect a local branch that exists on the remote to streamline
review creation.

- Add integration branch listing command and wire it into the dialog
- Replace plain selects with searchable SelectMenu and improved UX
- Attempt to detect and suggest a matching local source branch when possible

src/App.svelte

@@ -5568,6 +5568,7 @@
       />
     {:else if activeView === "review-center"}
       <ReviewCenter
+        localRepositoryPath={activeRepoPath}
         language={appLanguage}
         integrations={gitIntegrationSettings}
         initialQuery={reviewCenterInitialQuery}