Fix two git operation bugs

- gitCommitAll: abort commit when staging (git add -A) fails, e.g.
  due to a stale .git/index.lock.  Previously the failure was ignored
  and commit proceeded on an empty or partial index.

- gitPull: remove explicit branch argument from git pull --rebase.
  Passing both remote and branch can conflict with the branch's
  configured tracking ref, causing 'Cannot rebase onto multiple
  branches'.  Now uses just --rebase <remote>, letting git resolve
  the tracking branch from config.

- Test: index.lock scenario verifies commit is aborted on staging
  failure.

test/GitCommitSpec.hs

@@ -54,6 +54,19 @@ spec = do
                 countAfter2 <- commitCount repo
                 countAfter2 `shouldBe` countBefore2
 
+        it "aborts commit when staging fails (e.g. index.lock exists)" $ do
+            logger <- testLogger
+            withTempGitRepo $ \repo -> do
+                -- Create a lock file to make git add -A fail
+                writeFile (repo </> ".git" </> "index.lock") "locked"
+                writeFile (repo </> "new.txt") "new file"
+                countBefore <- commitCount repo
+                (code, _, err) <- gitCommitAll logger repo
+                -- Staging fails, so commit should not happen
+                code `shouldSatisfy` (/= ExitSuccess)
+                err `shouldSatisfy` ("index.lock" `T.isInfixOf`)
+                commitCount repo `shouldReturn` countBefore
+
     describe "startup sync" $ do
         it "commits and pushes uncommitted changes on startup" $ do
             logger <- testLogger