feat: web automation wrapper (#1349), DATALINK table on web, System theme; honest decode accounting

Ported from 2c38de53 (#1717). Main already carries the hatch PDF draw
order fix (#1345), the numeric set_properties compare (#1348) and the
web open from bytes, so those parts stay out; what remains:

#1349 — window.ocsControl.ready/request promise wrapper with an
ocs-ready event (web/ocs-control.js, loaded by the web page), and the
startup donation prompt is suppressed once a control request is seen
(opt-in pre-boot via localStorage["opencadstudio.automation"] = "1").
docs/automation/web.md documents both. The control protocol stays at 1.

DATALINK CSV-to-table works on web (picker + bytes through the session
registry — was std::fs, silently dead); COLORSCHEME accepts System
(prefers-color-scheme on web, AppsUseLightTheme on Windows).

Decode accounting, made honest per the fix-of-fix review: into_rgba8
allocates the RGBA destination while the native buffer is alive for
every non-Rgba8 layout (L8 5, La8 6, Rgb8 7, L16 6, La16 8 B/px
peaks — the formula now says so), GIF bills the screen+frame
coexistence at 8 B/px, and TIFF drops the 3x multipliers both ways —
tiff 0.11 splits the given budget between frame and scratch (a total
ceiling), so the old double-billing refused honest 16-bit GeoTIFFs
~2.25x early while admitting hostile chunk transients at 3x.

(cherry picked from commit 2c38de53)

src/app/annotation_data.rs

@@ -1298,6 +1298,34 @@ impl OpenCADStudio {
         Task::none()
     }
 
+    /// Web DATALINK: the picked .csv's bytes arrived. They are registered in
+    /// the picked-source registry — so `DATALINKUPDATE` re-reads them
+    /// in-session instead of failing on the absent filesystem — and fed to
+    /// the same table-insert path the native typed-path command uses.
+    #[cfg(target_arch = "wasm32")]
+    pub(super) fn on_datalink_csv_picked(
+        &mut self,
+        picked: Option<(String, Vec<u8>)>,
+    ) -> Task<Message> {
+        let Some((name, bytes)) = picked else {
+            return Task::none();
+        };
+        let text = String::from_utf8_lossy(&bytes).into_owned();
+        if !register_picked_source(&name, Arc::new(bytes)) {
+            if let Some(name) = take_last_collision().take() {
+                self.command_line.push_warning(
+                    crate::tf!(
+                        "\"{name}\" is already loaded with different contents; the existing file was kept."
+                    )
+                    .as_ref(),
+                );
+            }
+            return Task::none();
+        }
+        self.place_data_link_table(&text, &name);
+        Task::none()
+    }
+
     pub(super) fn on_data_link_browse(&mut self) -> Task<Message> {
         Task::perform(
             async {