feat(design): foundation pass — dusty violet palette, warm parchment light, Inter + JetBrains Mono

Applies the FabledSword + Scribe iteration palette to theme.css end to
end: indigo (#7c3aed) → dusty violet (#5B4A8A) accent, cool grey →
Obsidian/Iron/Pewter dark surfaces, warm parchment (#F5F1E8) light
mode, Inter body + JetBrains Mono code loaded alongside Fraunces, and
neutral hairline scrollbars (chrome is structural, not branded).

Adds the action token set (--color-action-primary Moss,
--color-action-secondary Bronze, --color-action-destructive Oxblood,
--color-action-ghost-border Pewter) but does not yet reclassify any
buttons — surface-phase work. Buttons remain dusty-violet gradients in
the meantime, by design.

Removes deprecated --color-accent-warm; replaces concrete usages with
--color-text-secondary (dates, flavor copy) or --color-warning (paused
status). Sweeps hardcoded indigo literals in component scoped CSS so
they don't bypass the token system.

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

frontend/src/components/AppHeader.vue

@@ -151,7 +151,7 @@ router.afterEach(() => {
 <style scoped>
 .app-header {
   background: linear-gradient(180deg, var(--color-surface), var(--color-bg));
-  border-bottom: 1px solid rgba(124, 58, 237, 0.18);
+  border-bottom: 1px solid rgba(91, 74, 138, 0.18);
   position: relative;
 }
 .nav {
@@ -220,8 +220,8 @@ router.afterEach(() => {
 .nav-link.router-link-active {
   color: var(--color-primary-solid);
   font-weight: 600;
-  background: rgba(124, 58, 237, 0.25);
-  box-shadow: 0 0 16px rgba(124, 58, 237, 0.3);
+  background: rgba(91, 74, 138, 0.25);
+  box-shadow: 0 0 16px rgba(91, 74, 138, 0.3);
 }
 
 /* Status indicator */