fix(theme): text on a filled colour needs its own token — the old one inverts

76 hardcoded `color: #fff` now resolve to --fs-text-on-action, a new token
that is parchment in BOTH modes.

The design system said they should supersede to --fs-text-primary, on the
recorded reasoning that "there is no 'text on action' colour, there is just the
text colour." That is true on dark and wrong on light. --fs-text-primary
inverts to #14171A; the surfaces underneath it do not invert at all — every one
of these 76 sits on an action colour, a semantic colour, the accent, or the CTA
gradient, all of which hold a single value across modes.

Sweeping as recorded would have put obsidian text on moss green: roughly 2.4:1,
against a house style whose stated floor is WCAG AA. It would have looked
correct to me, because I checked it in the mode where it was correct.

--color-accent-fg had the same defect independently and is repointed too.

The token check now reports zero superseded literals, down from 30 files, and
raw colour literals drop 246 -> 169.

Closes #2275.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UaYUaouG9jjhATyuxCKrQs

frontend/src/views/ProjectListView.vue

@@ -287,7 +287,7 @@ function overallPct(project: Project): { total: number; pct: number } {
 .btn-primary {
   padding: 0.45rem 1rem;
   background: var(--color-action-primary);
-  color: #fff;
+  color: var(--fs-text-on-action);
   border: none;
   border-radius: var(--radius-sm);
   cursor: pointer;
@@ -341,7 +341,7 @@ function overallPct(project: Project): { total: number; pct: number } {
 .empty-title { font-size: 1rem; font-weight: 500; color: var(--color-text-secondary); margin: 0 0 0.35rem; }
 .empty-sub { font-size: 0.85rem; margin: 0 0 1rem; }
 .empty-action { display: inline-block; padding: 0.4rem 1rem; border: 1px solid var(--color-primary); border-radius: var(--radius-sm); color: var(--color-primary); background: none; cursor: pointer; font-size: 0.85rem; transition: background 0.15s, color 0.15s; }
-.empty-action:hover { background: var(--color-primary); color: #fff; }
+.empty-action:hover { background: var(--color-primary); color: var(--fs-text-on-action); }
 
 .skeleton-card {
   height: 140px;
@@ -594,7 +594,7 @@ function overallPct(project: Project): { total: number; pct: number } {
 .modal-btn-primary {
   background: var(--color-primary);
   border-color: var(--color-primary);
-  color: #fff;
+  color: var(--fs-text-on-action);
 }
 .modal-btn-primary:hover:not(:disabled) {
   opacity: 0.9;