fix(ui): semantic turquoise tokens, badge styling, saved fade animation

- Add turquoise/turquoise-fg semantic color tokens to layout.css
  (light + dark mode), replacing all hardcoded #00C7B1 in components
- Bump Details toggle from text-xs to text-sm for visual hierarchy
- Block badge: navy → turquoise, overlapping top-left card border
  with absolute positioning to visually link PDF annotation badges
- Saved indicator: smooth 300ms opacity fade before removal
  (new 'fading' state in SaveState type)
- Transcribe buttons: use border-turquoise/bg-turquoise/text-turquoise-fg

Fixes @Leonie concerns: toggle visual weight, semantic tokens,
badge styling, saved fade animation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/layout.css

@@ -59,6 +59,10 @@
 	/* Header surface — independent from canvas/surface for per-mode control */
 	--color-header: var(--c-header);
 
+	/* Turquoise — transcription mode accent */
+	--color-turquoise: var(--c-turquoise);
+	--color-turquoise-fg: var(--c-turquoise-fg);
+
 	/* Focus ring — keyboard focus indicator, mode-aware (navy in light, mint in dark) */
 	--color-focus-ring: var(--c-focus-ring);
 
@@ -93,6 +97,9 @@
 	/* Header is brand-navy in light mode; same in dark mode for contrast compliance */
 	--c-header: #012851;
 
+	--c-turquoise: #00c7b1;
+	--c-turquoise-fg: #ffffff;
+
 	/* Focus ring: brand-navy in light mode — 14:1 on white, ~11:1 on sand */
 	--c-focus-ring: #012851;
 
@@ -132,6 +139,9 @@
 		/* Header at brand-navy: 4.99:1 with ink-3 (WCAG AA ✓), visually above canvas */
 		--c-header: #012851;
 
+		--c-turquoise: #00c7b1;
+		--c-turquoise-fg: #012851;
+
 		/* Focus ring: brand-mint in dark mode — 9.2:1 on canvas, 7.1:1 on surface */
 		--c-focus-ring: #a1dcd8;
 
@@ -167,6 +177,9 @@
 	/* Header at brand-navy: 4.99:1 with ink-3 (WCAG AA ✓), visually above canvas */
 	--c-header: #012851;
 
+	--c-turquoise: #00c7b1;
+	--c-turquoise-fg: #012851;
+
 	/* Focus ring: brand-mint in dark mode — 9.2:1 on canvas, 7.1:1 on surface */
 	--c-focus-ring: #a1dcd8;