fix(ci): address Windows test failures and timeout

- Extract inode function to platform-specific files (inode_unix.go,
  inode_windows.go) to fix syscall.Stat_t compile error on Windows
- Add skipOnWindows helper and skip Unix permission/symlink tests
  on Windows where chmod semantics differ
- Increase Windows test timeout from 10m to 20m since full test
  suite runs slower without race detector

Fixes Windows CI failures introduced when PR #904 expanded Windows
testing from smoke tests to full test suite.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/doctor/fix/e2e_test.go

@@ -815,6 +815,9 @@ func TestMergeDriverWithLockedConfig_E2E(t *testing.T) {
 
 // TestPermissionsWithWrongPermissions_E2E tests fixing wrong permissions on .beads
 func TestPermissionsWithWrongPermissions_E2E(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("skipping Unix permission test on Windows")
+	}
 	if os.Getuid() == 0 {
 		t.Skip("skipping permission tests when running as root")
 	}