fix(tests): create main branch after initial commit for worktree tests

Tests were failing because git worktree add -b branch worktree origin/main
requires origin/main to exist. Now all test setups create main branch after
initial commit so cloned repos have the expected branch.

tests/git_test.go

@@ -47,6 +47,12 @@ func TestGitCloneAndFetch(t *testing.T) {
 		t.Fatalf("git commit failed: %v", err)
 	}
 
+	// Create main branch (required for worktree operations)
+	cmd = exec.Command("git", "-C", sourceDir, "checkout", "-b", "main")
+	if err := cmd.Run(); err != nil {
+		t.Fatalf("git checkout -b main failed: %v", err)
+	}
+
 	// Test clone into empty path
 	ctx := context.Background()
 	err := action.CloneRepoActivity(ctx, action.CloneRepoInput{
@@ -124,6 +130,12 @@ func TestGitWorktreeAdd(t *testing.T) {
 		t.Fatalf("git commit failed: %v", err)
 	}
 
+	// Create main branch (required for worktree operations)
+	cmd = exec.Command("git", "-C", sourceDir, "checkout", "-b", "main")
+	if err := cmd.Run(); err != nil {
+		t.Fatalf("git checkout -b main failed: %v", err)
+	}
+
 	// Clone the repo
 	ctx := context.Background()
 	err := action.CloneRepoActivity(ctx, action.CloneRepoInput{
@@ -186,6 +198,12 @@ func TestGitCommit(t *testing.T) {
 		t.Fatalf("git commit failed: %v", err)
 	}
 
+	// Create main branch (required for worktree operations)
+	cmd = exec.Command("git", "-C", sourceDir, "checkout", "-b", "main")
+	if err := cmd.Run(); err != nil {
+		t.Fatalf("git checkout -b main failed: %v", err)
+	}
+
 	// Clone the repo
 	ctx := context.Background()
 	err := action.CloneRepoActivity(ctx, action.CloneRepoInput{