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/assets/editor-shared.css

@@ -52,18 +52,18 @@
 }
 .btn-save {
   padding: 0.45rem 1.1rem;
-  background: linear-gradient(135deg, #6366f1, #4f46e5);
+  background: linear-gradient(135deg, #5B4A8A, #3F3560);
   color: #fff;
   border: none;
   border-radius: var(--radius-sm);
   cursor: pointer;
   font-weight: 600;
   font-size: 0.875rem;
-  box-shadow: 0 2px 8px rgba(99, 102, 241, 0.28);
+  box-shadow: 0 2px 8px rgba(91, 74, 138, 0.28);
   transition: box-shadow 0.15s, opacity 0.15s;
 }
 .btn-save:hover:not(:disabled) {
-  box-shadow: 0 4px 14px rgba(99, 102, 241, 0.42);
+  box-shadow: 0 4px 14px rgba(91, 74, 138, 0.42);
   opacity: 0.95;
 }
 .btn-save:disabled {