feat(design): surface phase PR 7 — edge surfaces polish

Per the spec, the final per-surface PR bundles the smaller / chrome-y /
library-driven views (Header / Home / Calendar / Graph) together with
EventSlideOver since it's the calendar's primary interaction surface.

Button reclassification per Hybrid rule
- CalendarView btn-new-event: accent gradient → Moss action-primary.
  Creating an event is a workflow action, not a brand moment.
- EventSlideOver btn-primary (Save): accent gradient → Moss
- EventSlideOver btn-secondary (Cancel/No): muted ghost → Bronze
  action-secondary
- EventSlideOver btn-danger-ghost (Delete): hardcoded #ef4444 →
  --color-action-destructive ghost (with filled hover)
- EventSlideOver btn-danger (confirm Delete): hardcoded #ef4444 →
  --color-action-destructive filled

Brand-moment CTAs kept on accent
- HomeView btn-workspace-hero: home-page hero CTA into the active
  project — central brand-moment surface, gradient stays
- HomeView btn-workspace-sm: per-card workspace icon with the
  accent-tinted bg + hover-to-accent pattern, kept

Two-weights-only
- Snapped every font-weight 600/700 to 500 across the bundle
  (HomeView, GraphView, CalendarView, AppHeader, EventSlideOver).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/components/AppHeader.vue

@@ -174,7 +174,7 @@ router.afterEach(() => {
   font-family: 'Fraunces', Georgia, serif;
   font-style: italic;
   font-optical-sizing: auto;
-  font-weight: 600;
+  font-weight: 500;
   font-size: 1rem;
   letter-spacing: -0.01em;
   color: #c4b0f0;
@@ -219,7 +219,7 @@ router.afterEach(() => {
 }
 .nav-link.router-link-active {
   color: var(--color-primary-solid);
-  font-weight: 600;
+  font-weight: 500;
   background: rgba(91, 74, 138, 0.25);
   box-shadow: 0 0 16px rgba(91, 74, 138, 0.3);
 }
@@ -294,7 +294,7 @@ router.afterEach(() => {
 }
 .admin-badge {
   font-size: 0.65rem;
-  font-weight: 700;
+  font-weight: 500;
   text-transform: uppercase;
   letter-spacing: 0.05em;
   color: var(--color-primary);