Windows: resize border from the first frame, DPI-correct window moves (#1396)

* Windows: resize border from the first frame, DPI-correct window moves (#1381)

- The egui resize zones were laid out after the start page's early return, so a launch without
  a design had no resize edges at all. They now run on every page.
- Windows: the main window's procedure answers WM_NCHITTEST with the resize edges and corners,
  Windows' own border width at the window's DPI (8 px at 100 %), so the OS shows its resize
  cursors and runs its own resize (snap included) from the first message; no egui zones there.
- Windows: WM_GETDPISCALEDSIZE returns the size winit then applies (same logical size), so the
  rect the OS suggests while the title bar is dragged onto a monitor with another scale is the
  rect the window gets.
- Zone sizes and hit test shared in titlebar.rs and unit-tested; Windows CI checks the hit test
  right after launch and a real edge drag.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* Windows resize smoke: find the main window by its title

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* Windows resize smoke: probe the maximized window at the screen's edge

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

apps/solidcraft/src/main.rs

@@ -21,6 +21,8 @@ mod app_icon;
 mod control_server;
 #[cfg(target_os = "windows")]
 mod native_crash;
+#[cfg(target_os = "windows")]
+mod native_frame;
 #[cfg(target_os = "macos")]
 mod open_documents;
 #[cfg(any(target_os = "windows", target_os = "linux"))]
@@ -465,6 +467,15 @@ fn main() -> eframe::Result {
             let mut app = SolveApp::new(Session::default(), services(cc));
             app.apply_off_thread = Some(solidcraft_ui_egui::dialogs::APPLY_AT_ONCE);
             app.custom_titlebar = CUSTOM_TITLEBAR;
+            // Windows: the OS hit test offers the resize border, at the window's DPI, from the
+            // first message (#1381).
+            #[cfg(target_os = "windows")]
+            {
+                app.native_resize_border = CUSTOM_TITLEBAR && native_frame::install(cc);
+                if CUSTOM_TITLEBAR && !app.native_resize_border {
+                    eprintln!("SolidCraft window: no native resize border; egui edge zones instead");
+                }
+            }
             app.integrated_titlebar = cfg!(target_os = "macos");
             app.cpu_meshing = safe_mode;
             if let Some(p) = cc.storage.and_then(|s| solidcraft_ui_egui::prefs::stored(|k| s.get_string(k))).filter(|_| !safe_mode) {