feat(theme): overarching light-theme contrast (buttons, dividers, accent bars)

From the theme sweep review, three overarching light-theme fixes:
- Buttons: bump ImGuiCol_Button light overlays 13/20/28% -> 16/23/30% so the
  small/secondary buttons read as clearly as the main ones.
- Dividers + outlines: raise --divider (0.12-0.14 -> 0.20) and --outline
  (-> 0.24) across all light skins so section/list dividers are visible on white.
- Ratio/balance bars: deepen the muted --success/--warning greens/ambers in the
  light skins that were pale (light, marble, dune) so the shielded/transparent
  bars + success text are vivid (color-pop-light + iridescent were already vivid).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

res/themes/color-pop-light.toml

@@ -27,8 +27,8 @@ images = { background_image = "backgrounds/texture/pop-light_bg.png", logo = "lo
 --on-success = "#FFFFFF"
 --warning = "#E09020"
 --on-warning = "#000000"
---divider = "rgba(30,30,60,0.12)"
---outline = "rgba(30,30,60,0.15)"
+--divider = "rgba(30,30,60,0.20)"
+--outline = "rgba(30,30,60,0.24)"
 --scrim = "rgba(0,0,0,0.45)"
 --surface-hover = "rgba(96,64,224,0.05)"
 --surface-alt = "rgba(96,64,224,0.02)"

res/themes/dune.toml

@@ -24,12 +24,12 @@ elevation = { --elevation-0 = "#FDF8F0", --elevation-1 = "#F5EDE0", --elevation-
 --on-surface-disabled = "rgba(58,46,34,0.52)"
 --error = "#A0524A"
 --on-error = "#FFFFFF"
---success = "#6A8A5C"
+--success = "#4E8A42"
 --on-success = "#FFFFFF"
 --warning = "#C08840"
 --on-warning = "#000000"
---divider = "rgba(140,110,70,0.14)"
---outline = "rgba(140,110,70,0.16)"
+--divider = "rgba(140,110,70,0.20)"
+--outline = "rgba(140,110,70,0.24)"
 --scrim = "rgba(30,20,10,0.45)"
 --surface-hover = "rgba(176,120,64,0.06)"
 --surface-alt = "rgba(176,120,64,0.03)"

res/themes/iridescent.toml

@@ -28,8 +28,8 @@ elevation = { --elevation-0 = "#FDFBFF", --elevation-1 = "#F5F0FA", --elevation-
 --on-success = "#FFFFFF"
 --warning = "#E65100"
 --on-warning = "#000000"
---divider = "rgba(120,80,160,0.12)"
---outline = "rgba(120,80,160,0.14)"
+--divider = "rgba(120,80,160,0.20)"
+--outline = "rgba(120,80,160,0.24)"
 --scrim = "rgba(20,10,30,0.45)"
 --surface-hover = "rgba(140,107,175,0.06)"
 --surface-alt = "rgba(140,107,175,0.03)"

res/themes/light.toml

@@ -23,12 +23,12 @@ elevation = { --elevation-0 = "#FAFAFA", --elevation-1 = "#F2F3F5", --elevation-
 --on-surface-disabled = "rgba(42,44,48,0.52)"
 --error = "#8C5A62"
 --on-error = "#FFFFFF"
---success = "#5A7E5C"
+--success = "#3D7A42"
 --on-success = "#FFFFFF"
---warning = "#8A7A52"
+--warning = "#9A7A2E"
 --on-warning = "#000000"
---divider = "rgba(42,44,48,0.12)"
---outline = "rgba(42,44,48,0.14)"
+--divider = "rgba(42,44,48,0.20)"
+--outline = "rgba(42,44,48,0.24)"
 --scrim = "rgba(0,0,0,0.42)"
 --surface-hover = "rgba(42,44,48,0.04)"
 --surface-alt = "rgba(42,44,48,0.02)"

res/themes/marble.toml

@@ -24,12 +24,12 @@ elevation = { --elevation-0 = "#FAFAF8", --elevation-1 = "#F0EEEC", --elevation-
 --on-surface-disabled = "rgba(44,42,40,0.52)"
 --error = "#8C5250"
 --on-error = "#FFFFFF"
---success = "#5C7A62"
+--success = "#3F7A48"
 --on-success = "#FFFFFF"
---warning = "#8A7A4C"
+--warning = "#9A7A2E"
 --on-warning = "#000000"
---divider = "rgba(80,75,68,0.12)"
---outline = "rgba(80,75,68,0.14)"
+--divider = "rgba(80,75,68,0.20)"
+--outline = "rgba(80,75,68,0.24)"
 --scrim = "rgba(20,18,16,0.42)"
 --surface-hover = "rgba(110,117,128,0.05)"
 --surface-alt = "rgba(110,117,128,0.025)"

src/ui/material/color_theme.cpp

@@ -420,10 +420,11 @@ void ApplyColorThemeToImGui(const ColorTheme& theme)
         colors[ImGuiCol_ButtonHovered]    = ImVec4(1.0f, 1.0f, 1.0f, 30.0f / 255.0f);
         colors[ImGuiCol_ButtonActive]     = ImVec4(1.0f, 1.0f, 1.0f, 45.0f / 255.0f);
     } else {
-        // Darker overlays on light themes — the old 5/8/12% were barely-there grey and washed out.
-        colors[ImGuiCol_Button]           = ImVec4(0, 0, 0, 0.13f);
-        colors[ImGuiCol_ButtonHovered]    = ImVec4(0, 0, 0, 0.20f);
-        colors[ImGuiCol_ButtonActive]     = ImVec4(0, 0, 0, 0.28f);
+        // Darker overlays on light themes — the old 5/8/12% were barely-there grey and washed out;
+        // bumped again so the small/secondary buttons read as clearly as the main ones.
+        colors[ImGuiCol_Button]           = ImVec4(0, 0, 0, 0.16f);
+        colors[ImGuiCol_ButtonHovered]    = ImVec4(0, 0, 0, 0.23f);
+        colors[ImGuiCol_ButtonActive]     = ImVec4(0, 0, 0, 0.30f);
     }
     
     // Headers (collapsing headers, tree nodes, selectable, menu items)