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/commands/view.rs

@@ -535,7 +535,8 @@ impl OpenCADStudio {
                     "Available themes: {}",
                     "DARK LIGHT DRACULA NORD SOLARIZED_LIGHT SOLARIZED_DARK \
                      GRUVBOX_LIGHT GRUVBOX_DARK TOKYONIGHT TOKYONIGHTSTORM TOKYONIGHTLIGHT \
-                     KANAGAWAWAVE KANAGAWADRAGON KANAGAWALOTUS MOONFLY NIGHTFLY OXOCARBON FERRA",
+                     KANAGAWAWAVE KANAGAWADRAGON KANAGAWALOTUS MOONFLY NIGHTFLY OXOCARBON FERRA \
+                     SYSTEM (follows the OS or browser color scheme)",
                 ));
                 self.command_line.push_info(&crate::tf!(
                     "Current color scheme: <{}>",
@@ -559,7 +560,8 @@ impl OpenCADStudio {
                     self.command_line.push_output(&crate::tf!("Available themes: {}",
                         "DARK LIGHT DRACULA NORD SOLARIZED_LIGHT SOLARIZED_DARK \
                          GRUVBOX_LIGHT GRUVBOX_DARK TOKYONIGHT TOKYONIGHTSTORM TOKYONIGHTLIGHT \
-                         KANAGAWAWAVE KANAGAWADRAGON KANAGAWALOTUS MOONFLY NIGHTFLY OXOCARBON FERRA",
+                         KANAGAWAWAVE KANAGAWADRAGON KANAGAWALOTUS MOONFLY NIGHTFLY OXOCARBON FERRA \
+                         SYSTEM (follows the OS or browser color scheme)",
                     ));
                     return Some(Task::none());
                 }
@@ -569,6 +571,29 @@ impl OpenCADStudio {
                     );
                     return Some(Task::none());
                 }
+                // SYSTEM keeps its own name in the saved config and resolves
+                // to a concrete Light/Dark theme at run time — the browser's
+                // prefers-color-scheme on the web, the Windows personalization
+                // setting natively. Re-running the command re-resolves; there
+                // is no live preference listener.
+                if upper_sub == "SYSTEM" {
+                    if self.ui_theme.name == "Custom" {
+                        self.saved_custom_palette = Some(self.ui_theme.palette);
+                    }
+                    let resolved = crate::app::config::resolve_system_theme();
+                    let name = format!("{resolved:?}");
+                    self.ui_theme.name = "System".to_string();
+                    self.ui_theme.palette =
+                        crate::app::config::UiThemePalette::from_iced(resolved.seed());
+                    self.theme_color_inputs = self.ui_theme.palette.hex_values();
+                    self.active_theme = resolved;
+                    self.sync_model_space_theme(true);
+                    self.persist_settings_if_changed();
+                    self.command_line.push_output(crate::tf!(
+                        "Color scheme set to 'System' (currently {name})."
+                    ).as_ref());
+                    return Some(Task::none());
+                }
                 let theme = crate::app::config::parse_theme_name(sub);
                 if let Some(t) = theme {
                     if self.ui_theme.name == "Custom" {