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/lib/components/TranscriptionEditView.svelte

@@ -4,7 +4,7 @@ import { SvelteMap } from 'svelte/reactivity';
 import TranscriptionBlock from './TranscriptionBlock.svelte';
 import type { TranscriptionBlockData } from '$lib/types';
 
-type SaveState = 'idle' | 'saving' | 'saved' | 'error';
+type SaveState = 'idle' | 'saving' | 'saved' | 'fading' | 'error';
 
 type Props = {
 	blocks: TranscriptionBlockData[];
@@ -50,7 +50,12 @@ async function executeSave(blockId: string) {
 function scheduleSavedFade(blockId: string) {
 	setTimeout(() => {
 		if (getSaveState(blockId) === 'saved') {
-			setSaveState(blockId, 'idle');
+			setSaveState(blockId, 'fading');
+			setTimeout(() => {
+				if (getSaveState(blockId) === 'fading') {
+					setSaveState(blockId, 'idle');
+				}
+			}, 300);
 		}
 	}, 2000);
 }