fix(windows-clippy): pf-frame SAFETY comments + checked_div, pf-clipboard SAFETY placement + Gdi feature

Surfaced by giving windows-host CI its missing pf-encode/pf-frame path triggers:
the T2.3 auto-gate (dxgi.rs) and the clipboard host (windows.rs) landed with
Windows clippy owed — three undocumented unsafe blocks, one manual checked
division, one comment orphaned off its statement, and a latent E0432 in
standalone pf-clipboard builds (WNDCLASSW needs Win32_Graphics_Gdi; the host
graph only compiled via feature unification).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/pf-clipboard/Cargo.toml

@@ -42,6 +42,10 @@ wayland-protocols = { version = "0.32", features = ["client", "staging"] }
 # delayed rendering (`WM_RENDERFORMAT`) for text / CF_HTML / RTF / PNG.
 windows = { version = "0.62", features = [
     "Win32_Foundation",
+    # WNDCLASSW/RegisterClassW reference HBRUSH/HICON/HCURSOR, so windows-rs only generates
+    # them with the Gdi feature on. The host build got it via workspace feature-unification;
+    # a standalone `cargo check -p pf-clipboard` didn't (E0432) — declare it honestly.
+    "Win32_Graphics_Gdi",
     "Win32_System_DataExchange",
     "Win32_System_LibraryLoader",
     "Win32_System_Memory",