feat(git): add opt-in for unrelated histories during pull

Allow pulling repositories with unrelated commit histories when the user
explicitly opts in. The pull argument construction was refactored and
branch resolution made more robust so the backend can include the
--allow-unrelated-histories flag when requested.

- Extract pull argument logic and add support for allowing unrelated histories.
- Prompt users in the UI to confirm merging separate histories and retry pull.
- Restyle and improve the update toast UI for better layout and responsiveness.

src/lib/git.ts

@@ -405,8 +405,24 @@ export function commitAiSplit(path: string, options: CommitAiGenerateOptions): P
   });
 }
 
-export function pull(path: string, username?: string, password?: string, strategy: PullStrategy = "merge", remote?: string, branch?: string): Promise<GitStatus> {
-  return invoke<GitStatus>("pull", { path, username: username ?? null, password: password ?? null, strategy, remote: remote || null, branch: branch || null });
+export function pull(
+  path: string,
+  username?: string,
+  password?: string,
+  strategy: PullStrategy = "merge",
+  remote?: string,
+  branch?: string,
+  allowUnrelatedHistories = false,
+): Promise<GitStatus> {
+  return invoke<GitStatus>("pull", {
+    path,
+    username: username ?? null,
+    password: password ?? null,
+    strategy,
+    remote: remote || null,
+    branch: branch || null,
+    allowUnrelatedHistories,
+  });
 }
 
 export function fetchRemote(path: string, username?: string, password?: string, prune = false, remote?: string): Promise<GitStatus> {