test(services): add IsVendorIgnored regression tests

Tests verify that vendor/ detection from .gitignore works correctly:
- Detects 'vendor' and 'vendor/' patterns
- Handles comments and empty lines
- Correctly returns false when .gitignore is missing
- Correctly returns false when vendor is not in .gitignore

Covers the fix for auto-creating vendor/ in Go worktrees when vendor/
is explicitly gitignored by the project.

Author: jadb

test/e2e/deps_bootstrap_test.go

@@ -319,3 +319,4 @@ func TestAdd_GoProject_NoDepsMessageWhenNoPM(t *testing.T) {
 		t.Errorf("port output shown for Go project with no Docker: %s", combined)
 	}
 }
+