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/ChatMessage.vue

@@ -175,7 +175,7 @@ const timingParts = computed((): string[] => {
 
 .thinking-block {
   margin-bottom: 0.5rem;
-  border-left: 2px solid rgba(129, 140, 248, 0.35);
+  border-left: 2px solid rgba(91, 74, 138, 0.35);
   border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
   overflow: hidden;
 }