UI polish: Illuminated Transcript design language

- Fraunces serif for headings and assistant identity label
- Chat bubbles flipped: assistant responses elevated (card + left indigo
  accent + shadow), user prompts ghosted (transparent bg, muted text)
- AppLogo: book fill changed from text-color to indigo in light mode
- AppHeader: border-bottom removed; active nav uses underline accent
- NoteCard/TaskCard: border replaced with whisper indigo-tint shadow
- HomeView: dashboard-response uses left accent; progress bars indigo;
  empty-state decorative marker; project cards use shadow depth
- NotesListView: btn-new/btn-cta use indigo gradient + glow
- All primary CTA buttons: indigo gradient (135deg #6366f1 → #4f46e5)
  with box-shadow glow on hover
- Dark palette: navy (#1a1a2e family) → slate-indigo (#111113 family)
- Scrollbars: thin 4px indigo-tinted

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

frontend/src/components/AppHeader.vue

@@ -166,7 +166,6 @@ onUnmounted(() => document.removeEventListener("click", handleClickOutside));
 <style scoped>
 .app-header {
   background: var(--color-bg-secondary);
-  border-bottom: 1px solid var(--color-border);
   position: relative;
 }
 .nav {
@@ -182,8 +181,11 @@ onUnmounted(() => document.removeEventListener("click", handleClickOutside));
   display: flex;
   align-items: center;
   gap: 0.4rem;
-  font-weight: 700;
-  font-size: 1.1rem;
+  font-family: 'Fraunces', Georgia, serif;
+  font-optical-sizing: auto;
+  font-weight: 600;
+  font-size: 1.15rem;
+  letter-spacing: -0.01em;
   color: var(--color-primary);
   text-decoration: none;
   flex-shrink: 0;
@@ -217,12 +219,13 @@ onUnmounted(() => document.removeEventListener("click", handleClickOutside));
 }
 .nav-link:hover {
   color: var(--color-primary);
-  background: var(--color-bg-card);
+  background: color-mix(in srgb, var(--color-primary) 8%, transparent);
 }
 .nav-link.router-link-active {
   color: var(--color-primary);
-  background: var(--color-bg-card);
   font-weight: 600;
+  box-shadow: inset 0 -2px 0 var(--color-primary);
+  border-radius: 0;
 }
 
 /* Status indicator */