refactor(theme): remove 184 var() fallbacks — every one was unreachable

#2277 counted ~150 "raw colour literals bypassing the tokens". Measuring them
told a different story: 184 sat in `var(--token, #fallback)` position, and a
check against theme.css shows every one of those tokens IS declared. So the
fallbacks could not render. Not drift — vestigial.

They were also not this palette. The most common were Tailwind and Flat-UI
defaults — #6366f1 indigo, #22c55e green, #f59e0b amber, #3b82f6 blue,
#e74c3c and #27ae60 — a second, unsanctioned colour scheme sitting in the
codebase looking like the app's colours to anyone reading it.

Removing them is not tidying. #2319's lesson is that a fallback is WORSE than a
missing token: a missing token renders as nothing and someone eventually
notices, while a fallback renders something plausible forever. These 184 were
one token rename away from silently repainting the app in Tailwind. The design
token check would catch the rename — but the fallback is precisely the thing
that would make it invisible if the check were ever bypassed.

Literal count 152 -> 45, which matters beyond the number: a report that is
mostly unreachable noise is one people stop reading, and then it stops working
while still passing. What remains should be genuinely worth looking at.

Done with a paren-aware transform, not a regex — `var(--x, rgba(0,0,0,.5))`
nests parens and `[^)]+` would cut at the first one and leave `))` behind.
Verified after: every changed line is a fallback strip and nothing else, and
every var() reference still resolves.

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

frontend/src/views/TaskViewerView.vue

@@ -561,7 +561,7 @@ const subTaskProgress = computed(() => {
 }
 .subtasks-fill {
   height: 100%;
-  background: var(--color-status-done, #22c55e);
+  background: var(--color-status-done);
   border-radius: 2px;
   transition: width 0.3s ease;
 }
@@ -602,13 +602,13 @@ const subTaskProgress = computed(() => {
   border: 2px solid var(--color-text-muted);
 }
 .dot-in-progress {
-  background: var(--color-status-in-progress, #3b82f6);
+  background: var(--color-status-in-progress);
 }
 .dot-done {
-  background: var(--color-status-done, #22c55e);
+  background: var(--color-status-done);
 }
 .dot-cancelled {
-  background: var(--color-text-muted, #6b7280);
+  background: var(--color-text-muted);
 }
 .sub-title {
   flex: 1;
@@ -749,26 +749,26 @@ const subTaskProgress = computed(() => {
 
 /* ── Goal block + auto-summary banner ─────────────────────────────────────── */
 .task-goal-display {
-  border-left: 2px solid var(--color-border, rgba(255, 255, 255, 0.12));
+  border-left: 2px solid var(--color-border);
   padding: 0.4rem 0 0.4rem 0.9rem;
   margin: 0.75rem 0 1.25rem;
   background: rgba(255, 255, 255, 0.02);
 }
 .goal-label {
-  font-family: var(--font-display, "Fraunces", serif);
+  font-family: var(--font-display);
   font-style: italic;
   font-size: 0.78rem;
   font-weight: 500;
   letter-spacing: 0.04em;
   text-transform: uppercase;
-  color: var(--color-text-muted, rgba(255, 255, 255, 0.5));
+  color: var(--color-text-muted);
   margin: 0 0 0.25rem;
 }
 .goal-text {
   margin: 0;
   font-size: 0.95rem;
   line-height: 1.45;
-  color: var(--color-text, inherit);
+  color: var(--color-text);
   white-space: pre-wrap;
 }
 .auto-summary-banner {
@@ -777,11 +777,11 @@ const subTaskProgress = computed(() => {
   gap: 0.5rem;
   font-size: 0.78rem;
   font-style: italic;
-  color: var(--color-text-muted, rgba(255, 255, 255, 0.55));
+  color: var(--color-text-muted);
   margin: 0 0 0.75rem;
 }
 .auto-summary-icon {
-  color: var(--color-primary, #6366f1);
+  color: var(--color-primary);
   font-size: 0.85rem;
 }
 </style>