web: parse ?chrome= so an embedding host can leave out the title bar and File tab

#1877 added Chrome to SheetApp for hosts that embed the sheet natively, but the web build never set it: an iframe host that owns the files still draws the title bar it duplicates, and Backstage's Open/Save As can replace the document behind the host's back. Parse the flag where the other URL flags are parsed; the UI already honours Chrome, so nothing else changes.

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

apps/gridcraft-web/src/main.rs

@@ -11,8 +11,9 @@
 //! URL query flags: `?webgl` forces WebGL2; `?sample=sales|budget|grades` opens a sample;
 //! `?host=parent` (inside an `<iframe>`) talks to a same-origin parent page instead: it sends the
 //! workbook to open and stores what GridCraft saves (`host`), and `&author=` names the user for
-//! notes and comments. Preferences (theme, interface size, editing options…) are kept in
-//! `localStorage` (`prefs`).
+//! notes and comments. `?chrome=none|notitlebar|nofiletab` leaves the title bar and/or the File tab
+//! undrawn for a host that embeds the sheet in its own window (see `Chrome`). Preferences (theme,
+//! interface size, editing options…) are kept in `localStorage` (`prefs`).
 #![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]
 
 #[cfg(target_arch = "wasm32")]

apps/gridcraft-web/src/web.rs

@@ -60,6 +60,17 @@ pub fn start() {
                     }
                     let mut app = SheetApp::new(session, services);
                     app.ui.system_theme = true;
+                    // `?chrome=none|notitlebar|nofiletab`: a host that embeds the sheet in its own window and owns the files
+                    // can leave the title bar and/or the File tab undrawn (`Chrome`, #1877). An unknown value keeps
+                    // everything, as the default does.
+                    if let Some(chrome) = query_param("chrome") {
+                        match chrome.as_str() {
+                            "none" => app.chrome = gridcraft_ui_egui::Chrome { title_bar: false, file_tab: false },
+                            "notitlebar" => app.chrome.title_bar = false,
+                            "nofiletab" => app.chrome.file_tab = false,
+                            _ => {}
+                        }
+                    }
                     // Follow the browser's language, except a CJK one: the web build has no system
                     // CJK fonts (none are bundled), so that interface would render as tofu.
                     let browser = gridcraft_ui_egui::i18n::Language::system();

packaging/web/README.md

@@ -72,6 +72,10 @@ Local test: `python3 -m http.server 8765` inside the folder, then open http://lo
   `allow-same-origin` there's no storage. Without `allow-downloads`, Save and Export (browser
   downloads) are blocked.
 - Don't send `X-Frame-Options: DENY` or a `frame-ancestors` CSP that excludes the embedding page.
+- **Window chrome:** `?chrome=none` on the iframe `src` leaves out the title bar and the File tab
+  (whose Backstage view then never opens); `?chrome=notitlebar` or `?chrome=nofiletab` leave out just
+  one. Use them when the host window already shows the file name and owns the files, so the sheet's
+  own Open or Save As cannot replace what the host thinks is open. Everything stays on by default.
 
 ## Renderer selection