refactor(theme): the accent was hand-written 16 times — now derived

`rgba(91, 74, 138, …)` is Scribe's accent in decimal. It appears sixteen times
across five files at ten different opacities, plus once as #5B4A8A. Change the
accent in the design system and none of them would have moved — which is the
precise failure the token system exists to prevent, hiding in a notation that
does not look like a colour constant.

Now `color-mix(in srgb, var(--color-primary) N%, transparent)`, so every one
follows the accent. The design system already uses this form for its own tints
(--fs-accent-soft, -faint, -wash), so this is the established idiom rather than
a new one.

The CI literal count barely moves (45 -> 44) because its regex matches #hex and
fifteen of these were rgba(). Worth stating plainly: **the count was never the
goal, and the check is blind to this whole class.** An rgba triple is a colour
literal in every sense that matters and the report does not see it.

Not touched: the badge palette in KnowledgeView (#7A6DA8, #fbbf24, #818cf8 for
note/task/plan) and the remaining greys. Those are genuine unmade decisions —
what colour IS a plan badge — not drift, and inventing tokens for them would be
deciding by implementation.

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

frontend/src/components/AppHeader.vue

@@ -129,7 +129,7 @@ router.afterEach(() => {
 <style scoped>
 .app-header {
   background: linear-gradient(180deg, var(--color-surface), var(--color-bg));
-  border-bottom: 1px solid rgba(91, 74, 138, 0.18);
+  border-bottom: 1px solid color-mix(in srgb, var(--color-primary) 18%, transparent);
   position: relative;
 }
 .nav {
@@ -197,8 +197,8 @@ router.afterEach(() => {
 .nav-link.router-link-active {
   color: var(--color-primary-solid);
   font-weight: 500;
-  background: rgba(91, 74, 138, 0.25);
-  box-shadow: 0 0 16px rgba(91, 74, 138, 0.3);
+  background: color-mix(in srgb, var(--color-primary) 25%, transparent);
+  box-shadow: 0 0 16px color-mix(in srgb, var(--color-primary) 30%, transparent);
 }
 
 /* Status indicator */

frontend/src/components/NoteCard.vue

@@ -64,11 +64,11 @@ function goEdit() {
   text-decoration: none;
   color: inherit;
   background: var(--color-bg-card);
-  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.06), 0 0 0 1px rgba(91, 74, 138, 0.06);
+  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.06), 0 0 0 1px color-mix(in srgb, var(--color-primary) 6%, transparent);
   transition: box-shadow 0.2s, transform 0.18s ease;
 }
 .note-card:hover {
-  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.10), 0 0 0 1px rgba(91, 74, 138, 0.14);
+  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.10), 0 0 0 1px color-mix(in srgb, var(--color-primary) 14.0%, transparent);
   transform: translateY(-2px);
 }
 
@@ -89,7 +89,7 @@ function goEdit() {
 }
 .note-card.compact:hover {
   box-shadow: none;
-  background: rgba(91, 74, 138, 0.04);
+  background: color-mix(in srgb, var(--color-primary) 4%, transparent);
   transform: none;
 }
 .note-title-compact {

frontend/src/components/TaskCard.vue

@@ -112,11 +112,11 @@ function isOverdue(): boolean {
   text-decoration: none;
   color: inherit;
   background: var(--color-bg-card);
-  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.06), 0 0 0 1px rgba(91, 74, 138, 0.06);
+  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.06), 0 0 0 1px color-mix(in srgb, var(--color-primary) 6%, transparent);
   transition: box-shadow 0.2s, transform 0.18s ease;
 }
 .task-card:hover {
-  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.10), 0 0 0 1px rgba(91, 74, 138, 0.14);
+  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.10), 0 0 0 1px color-mix(in srgb, var(--color-primary) 14.0%, transparent);
   transform: translateY(-2px);
 }
 

frontend/src/views/KnowledgeView.vue

@@ -548,7 +548,7 @@ onUnmounted(() => {
   content: '· · ·';
   display: block;
   text-align: center;
-  color: rgba(91, 74, 138, 0.3);
+  color: color-mix(in srgb, var(--color-primary) 30%, transparent);
   font-size: 0.9rem;
   letter-spacing: 0.4em;
   padding: 4px 0 12px;
@@ -662,7 +662,7 @@ onUnmounted(() => {
   flex-shrink: 0;
 }
 .filter-btn.active .filter-count {
-  background: rgba(91, 74, 138, 0.2);
+  background: color-mix(in srgb, var(--color-primary) 20%, transparent);
   color: var(--color-primary);
 }
 .filter-tag { font-size: 0.78rem; }
@@ -749,12 +749,12 @@ onUnmounted(() => {
 }
 .k-card:hover {
   transform: translateY(-2px);
-  box-shadow: 0 8px 28px rgba(91, 74, 138, 0.25), 0 2px 8px rgba(0, 0, 0, 0.3);
-  border-color: rgba(91, 74, 138, 0.35);
+  box-shadow: 0 8px 28px color-mix(in srgb, var(--color-primary) 25%, transparent), 0 2px 8px rgba(0, 0, 0, 0.3);
+  border-color: color-mix(in srgb, var(--color-primary) 35%, transparent);
 }
 
 /* Type-specific card DNA */
-.k-card--note   { border-color: rgba(91, 74, 138, 0.20); }
+.k-card--note   { border-color: color-mix(in srgb, var(--color-primary) 20%, transparent); }
 .k-card--task   { border-color: rgba(212, 160, 23, 0.18); }
 
 /* Top gradient bars */
@@ -769,7 +769,7 @@ onUnmounted(() => {
 }
 .k-card--note::before {
   right: 0;
-  background: linear-gradient(90deg, #5B4A8A, #7A6DA8);
+  background: linear-gradient(90deg, var(--color-primary), #7A6DA8);
 }
 .k-card--task::before {
   right: 0;
@@ -788,7 +788,7 @@ onUnmounted(() => {
   text-transform: uppercase;
   letter-spacing: 0.04em;
 }
-.badge--note   { background: rgba(91, 74, 138,0.15); color: #7A6DA8; }
+.badge--note   { background: color-mix(in srgb, var(--color-primary) 15%, transparent); color: #7A6DA8; }
 .badge--task   { background: rgba(212,160,23,0.15); color: #fbbf24; }
 .badge--plan   { background: rgba(99,102,241,0.18); color: #818cf8; }
 

frontend/src/views/SettingsView.vue

@@ -2404,7 +2404,7 @@ function formatUserDate(iso: string): string {
 }
 .sidebar-item.active {
   color: var(--color-primary);
-  background: rgba(91, 74, 138, 0.08);
+  background: color-mix(in srgb, var(--color-primary) 8%, transparent);
   border-left-color: var(--color-primary);
   font-weight: 500;
 }