feat: in-app update notice — checks GitHub releases on startup

Adds a one-shot update check that runs on app boot and pops up a small
"Update Available" window when the GitHub releases API reports a newer
tag than this build's `CARGO_PKG_VERSION`.

- `src/update_check.rs` — async wrapper around a blocking `ureq` GET to
  `api.github.com/repos/HakanSeven12/H7CAD/releases/latest`, returns
  `Some(version)` when a newer release exists, `None` otherwise (silent
  on network / parse failure so a missing connection never blocks
  launch).
- `H7CAD::boot` chains a `Task::perform` next to the main-window open
  so the check runs in parallel with first-paint.
- New window plumbed like the other floating panels (page setup, about,
  etc.): `update_notice_window`/`update_notice_version` state, title
  entry, `OsWindowClosed` cleanup, and a `ui::update_notice::view_window`
  modal that shows installed vs. latest version plus "Later" /
  "Open Release Page" buttons. Open routes through `open::that` to the
  releases URL and dismisses the modal.

Dependency: adds `ureq = { version = "2", default-features = false,
features = ["tls"] }` — the smallest blocking HTTP client + TLS combo
that doesn't drag in an async runtime.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/app/mod.rs

@@ -98,6 +98,12 @@ pub(super) struct H7CAD {
     dimstyle_window: Option<window::Id>,
     shortcuts_window: Option<window::Id>,
     about_window: Option<window::Id>,
+    /// New-release notification window — opened on startup when the
+    /// GitHub releases API reports a newer version than this build.
+    update_notice_window: Option<window::Id>,
+    /// Tag of the latest available release (without the leading "v"),
+    /// e.g. `"0.3.0"`. `None` when up-to-date or check hasn't returned.
+    update_notice_version: Option<String>,
     /// In-memory clipboard: cloned entities waiting to be pasted.
     clipboard: Vec<acadrust::EntityType>,
     /// Centroid of the clipboard entities (XZ plane, Y-up).
@@ -529,6 +535,14 @@ pub enum Message {
     OsWindowClosed(window::Id),
     /// No-op — used as a fallback when a TabEvent has no host mapping.
     Noop,
+    /// GitHub releases API returned a result. `Some(version)` means a
+    /// newer release exists; we open the update-notice window.
+    UpdateCheckResult(Option<String>),
+    /// User dismissed the update-notice window.
+    UpdateNoticeClose,
+    /// User clicked the "Open release page" button — opens the GitHub
+    /// release URL in the OS default browser and closes the notice.
+    UpdateNoticeOpenRelease,
     // ── Page Setup ────────────────────────────────────────────────────────
     /// Open the Page Setup panel for the current layout.
     PageSetupOpen,
@@ -713,6 +727,8 @@ impl H7CAD {
             dimstyle_window: None,
             shortcuts_window: None,
             about_window: None,
+            update_notice_window: None,
+            update_notice_version: None,
             clipboard: Vec::new(),
             clipboard_centroid: glam::Vec3::ZERO,
             layout_context_menu: None,
@@ -810,8 +826,12 @@ impl H7CAD {
         });
         let mut s = state;
         s.main_window = Some(id);
-        let task = open_task.map(|_| Message::Noop);
-        (s, task)
+        let open_main = open_task.map(|_| Message::Noop);
+        let check_update = Task::perform(
+            crate::update_check::check_for_update(),
+            Message::UpdateCheckResult,
+        );
+        (s, Task::batch([open_main, check_update]))
     }
 }
 
@@ -851,6 +871,9 @@ pub fn run() -> iced::Result {
             if Some(window_id) == state.about_window {
                 return "About H7CAD".into();
             }
+            if Some(window_id) == state.update_notice_window {
+                return "Update Available".into();
+            }
             if Some(window_id) == state.unsaved_dialog_window {
                 return "Unsaved Changes".into();
             }

src/app/update.rs

@@ -974,6 +974,9 @@ impl H7CAD {
                 if self.about_window == Some(id) {
                     self.about_window = None;
                 }
+                if self.update_notice_window == Some(id) {
+                    self.update_notice_window = None;
+                }
                 Task::none()
             }
 
@@ -3536,6 +3539,37 @@ impl H7CAD {
                     Task::none()
                 }
             }
+            Message::UpdateCheckResult(latest) => {
+                let Some(version) = latest else {
+                    return Task::none();
+                };
+                self.update_notice_version = Some(version);
+                if let Some(id) = self.update_notice_window {
+                    return window::gain_focus(id);
+                }
+                let (id, task) = window::open(window::Settings {
+                    size: iced::Size::new(480.0, 240.0),
+                    resizable: false,
+                    ..Default::default()
+                });
+                self.update_notice_window = Some(id);
+                task.map(|_| Message::Noop)
+            }
+            Message::UpdateNoticeClose => {
+                if let Some(id) = self.update_notice_window.take() {
+                    window::close(id)
+                } else {
+                    Task::none()
+                }
+            }
+            Message::UpdateNoticeOpenRelease => {
+                let _ = open::that(crate::update_check::RELEASES_PAGE);
+                if let Some(id) = self.update_notice_window.take() {
+                    window::close(id)
+                } else {
+                    Task::none()
+                }
+            }
             Message::PageSetupWidthEdit(s) => {
                 self.page_setup_w = s;
                 Task::none()

src/app/view.rs

@@ -190,6 +190,13 @@ impl H7CAD {
         if Some(window_id) == self.about_window {
             return crate::ui::about::view_window();
         }
+        if Some(window_id) == self.update_notice_window {
+            let latest = self
+                .update_notice_version
+                .as_deref()
+                .unwrap_or("?");
+            return crate::ui::update_notice::view_window(latest);
+        }
         if Some(window_id) == self.unsaved_dialog_window {
             let tab_name = match &self.pending_close {
                 Some(super::PendingClose::Tab(idx)) => self