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The token check now reports zero superseded literals, down from 30 files, and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/SettingsView.vue

@@ -2567,7 +2567,7 @@ function formatUserDate(iso: string): string {
 .btn-save {
   padding: 0.4rem 0.9rem;
   background: var(--color-action-primary);
-  color: #fff;
+  color: var(--fs-text-on-action);
   border: none;
   border-radius: var(--radius-sm);
   cursor: pointer;
@@ -2595,7 +2595,7 @@ function formatUserDate(iso: string): string {
 }
 .btn-danger-outline:hover:not(:disabled) {
   background: var(--color-action-destructive);
-  color: #fff;
+  color: var(--fs-text-on-action);
 }
 .btn-danger-outline:disabled { opacity: 0.5; cursor: default; }
 
@@ -2603,7 +2603,7 @@ function formatUserDate(iso: string): string {
 .btn-danger {
   padding: 0.4rem 0.9rem;
   background: var(--color-action-destructive);
-  color: #fff;
+  color: var(--fs-text-on-action);
   border: none;
   border-radius: var(--radius-sm);
   cursor: pointer;
@@ -2620,7 +2620,7 @@ function formatUserDate(iso: string): string {
 .btn-secondary {
   padding: 0.4rem 0.9rem;
   background: var(--color-action-secondary);
-  color: #fff;
+  color: var(--fs-text-on-action);
   border: none;
   border-radius: var(--radius-sm);
   cursor: pointer;
@@ -2685,7 +2685,7 @@ function formatUserDate(iso: string): string {
 .db-health-table tr.dh-warn td:first-child code { color: var(--color-warning); }
 .btn-warn:hover:not(:disabled) {
   background: var(--color-warning);
-  color: #fff;
+  color: var(--fs-text-on-action);
 }
 
 .saved-msg {
@@ -3000,7 +3000,7 @@ function formatUserDate(iso: string): string {
 .btn-confirm-delete {
   padding: 0.25rem 0.6rem;
   background: var(--color-action-destructive);
-  color: #fff;
+  color: var(--fs-text-on-action);
   border: none;
   border-radius: var(--radius-sm);
   cursor: pointer;
@@ -3033,7 +3033,7 @@ function formatUserDate(iso: string): string {
   transition: background 0.15s;
 }
 .btn-toggle:disabled { opacity: 0.6; cursor: default; }
-.btn-toggle-open { background: var(--color-action-primary); color: #fff; }
+.btn-toggle-open { background: var(--color-action-primary); color: var(--fs-text-on-action); }
 .btn-toggle-open:hover:not(:disabled) { background: var(--color-action-primary-hover); }
 .btn-toggle-close {
   background: var(--color-bg-secondary);
@@ -3151,7 +3151,7 @@ function formatUserDate(iso: string): string {
 .btn-primary {
   padding: 0.4rem 0.9rem;
   background: var(--color-action-primary);
-  color: #fff;
+  color: var(--fs-text-on-action);
   border: none;
   border-radius: var(--radius-sm);
   cursor: pointer;
@@ -3391,7 +3391,7 @@ function formatUserDate(iso: string): string {
 }
 .unit-btn.active {
   background: var(--color-action-primary);
-  color: #fff;
+  color: var(--fs-text-on-action);
 }
 .unit-btn:hover:not(.active) {
   color: var(--color-text);
@@ -3863,7 +3863,7 @@ function formatUserDate(iso: string): string {
 }
 .btn-danger-outline:hover:not(:disabled) {
   background: var(--color-action-destructive);
-  color: #fff;
+  color: var(--fs-text-on-action);
 }
 .btn-danger-outline:disabled { opacity: 0.5; cursor: default; }
 @keyframes va-dot-bounce {