Theme FAB: transparent button bg on dark, add --theme-fab-btn-bg. Bump 03.09.32

Dark theme: icon button and auto switch background is transparent
on the off-white FAB. Light theme keeps subtle white overlay.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/media/css/theme/dark.standard.css

@@ -831,6 +831,7 @@ color-scheme: dark;
 /* ===== THEME FAB ===== */
 --theme-fab-bg: #e6ebf1;
 --theme-fab-color: #0e1318;
+--theme-fab-btn-bg: transparent;
 
 /* ===== OFFLINE PAGE ===== */
 --offline-card-bg: rgba(0, 0, 0, 0.6);

src/media/css/theme/light.standard.css

@@ -830,6 +830,7 @@ color-scheme: light;
 /* ===== THEME FAB ===== */
 --theme-fab-bg: var(--color-primary, #112855);
 --theme-fab-color: #fff;
+--theme-fab-btn-bg: rgba(255,255,255,.15);
 
 /* ===== OFFLINE PAGE ===== */
 --offline-card-bg: rgba(0, 0, 0, 0.55);