fix(ui): draw sketch constraint glyphs in red (#414)

* fix(ui): draw sketch constraint glyphs in red

Traditional CAD convention marks constraint glyphs in red. glyph_edge
and glyph_text in both themes now use red values. glyph_bg is
unchanged. The same glyph box switches to the error colour when a
constraint fails. The new reds are chosen to stay distinct from that
error colour. They are also distinct from the blue used for selection
and hover. See the pull request body for the before and after RGB
values and the contrast reasoning.

* fix(ui): match constraint toolbar icons to the red glyph colour

The CONSTRAINTS panel buttons and their drop-down rows drew their accent
strokes in the normal sketch tool green. They now use glyph_text, the same
red the matching constraint glyph box uses in the sketch view. A new
panel_accent helper in toolbar.rs picks the colour: the constraint red for
the CONSTRAINTS panel, the existing sketch green for every other sketch
tool, and the plain accent everywhere else. No other toolbar styling
changed.

crates/ui-egui/src/theme.rs

@@ -191,8 +191,8 @@ impl Tokens {
             subheading_bg: Color32::from_rgb(234, 237, 242),
             profile_fill: Color32::from_rgba_unmultiplied_const(255, 196, 120, 70),
             glyph_bg: Color32::WHITE,
-            glyph_edge: Color32::from_rgb(90, 150, 90),
-            glyph_text: Color32::from_rgb(40, 110, 40),
+            glyph_edge: Color32::from_rgb(190, 110, 100),
+            glyph_text: Color32::from_rgb(150, 40, 35),
             overlay: Color32::from_rgba_unmultiplied_const(255, 255, 255, 235),
             rubber_band: Color32::from_rgb(30, 120, 230),
             app_bar_text: Color32::from_rgb(230, 234, 242),
@@ -247,8 +247,8 @@ impl Tokens {
         t.heading_bg = Color32::from_rgb(38, 44, 55);
         t.subheading_bg = Color32::from_rgb(48, 55, 68);
         t.glyph_bg = Color32::from_rgb(44, 50, 60);
-        t.glyph_edge = Color32::from_rgb(96, 170, 110);
-        t.glyph_text = Color32::from_rgb(150, 220, 160);
+        t.glyph_edge = Color32::from_rgb(200, 130, 120);
+        t.glyph_text = Color32::from_rgb(240, 165, 155);
         t.overlay = Color32::from_rgba_unmultiplied_const(34, 38, 46, 240);
         t.rubber_band = Color32::from_rgb(92, 160, 255);
         t.timeline_item = Color32::from_rgb(52, 58, 70);