fix(gui): make the window background and weak-text colours actually apply

Two theme fields had no visible effect:
- window_bg mapped only to egui's window_fill, but the app draws on the bare
  background layer with no panel, so that's never painted — the real backdrop
  was a hardcoded GL clear colour. Paint a themed background rect (window_bg)
  behind everything in draw() instead.
- weak_text was dead: egui's weak_text_color() derives from the text colour
  unless Visuals::weak_text_color is set, which it wasn't. Set it.

Audited the rest (panel/input bg, text, accent, button, hover, and the five
status colours) — those already resolve to the right egui fields.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/gui/mod.rs

@@ -939,6 +939,17 @@ impl PixelPassApp {
             apply_theme(ui.ctx(), &self.theme.active);
             self.theme.dirty = false;
         }
+        // Paint the themed window background behind everything. The app draws on
+        // egui's bare background layer with no panel, so `window_fill` is never
+        // shown — without this the only backdrop is the GL clear colour, which
+        // the theme can't reach. Painted first, so it sits behind the widgets.
+        let bg = if self.theme.editing {
+            self.theme.draft.window_bg
+        } else {
+            self.theme.active.window_bg
+        };
+        ui.painter()
+            .rect_filled(ui.ctx().content_rect(), egui::CornerRadius::ZERO, bg);
         match self.screen {
             Screen::Menu => self.menu(ui),
             Screen::Host => self.host(ui),

src/gui/theme.rs

@@ -101,6 +101,9 @@ impl Theme {
         v.faint_bg_color = self.panel_bg;
         v.extreme_bg_color = self.input_bg;
         v.override_text_color = Some(self.text);
+        // `.weak()` text resolves via `weak_text_color()`, which derives from
+        // `text` unless this is set — so without it the weak-text field is dead.
+        v.weak_text_color = Some(self.weak_text);
         v.hyperlink_color = self.accent;
         v.error_fg_color = self.error;
         v.warn_fg_color = self.warning;