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/components/WorkspaceTaskPanel.vue

@@ -387,7 +387,7 @@ defineExpose({ reload: loadAll });
 
 .task-add-input {
   flex: 1;
-  background: var(--color-input-bg, var(--color-bg));
+  background: var(--color-input-bg);
   border: 1px solid var(--color-border);
   border-radius: 5px;
   padding: 0.28rem 0.5rem;
@@ -413,7 +413,7 @@ defineExpose({ reload: loadAll });
   gap: 0.4rem;
   width: 100%;
   padding: 0.4rem 0.65rem;
-  background: var(--color-surface-raised, color-mix(in srgb, var(--color-surface) 92%, var(--color-text)));
+  background: var(--color-surface-raised);
   border: none;
   cursor: pointer;
   text-align: left;
@@ -433,7 +433,7 @@ defineExpose({ reload: loadAll });
   text-transform: capitalize;
 }
 .ms-status-active { background: color-mix(in srgb, var(--color-primary) 15%, transparent); color: var(--color-primary); }
-.ms-status-completed { background: color-mix(in srgb, var(--color-success, #27ae60) 15%, transparent); color: var(--color-success, #27ae60); }
+.ms-status-completed { background: color-mix(in srgb, var(--color-success) 15%, transparent); color: var(--color-success); }
 
 .task-items {
   list-style: none;
@@ -466,7 +466,7 @@ defineExpose({ reload: loadAll });
   justify-content: center;
 }
 .status-dot.status-in_progress { border-color: var(--color-primary); color: var(--color-primary); }
-.status-dot.status-done { border-color: var(--color-success, #27ae60); color: var(--color-success, #27ae60); }
+.status-dot.status-done { border-color: var(--color-success); color: var(--color-success); }
 
 .task-title {
   flex: 1;
@@ -522,7 +522,7 @@ defineExpose({ reload: loadAll });
   margin-left: auto;
 }
 .status-badge.status-in_progress { border-color: var(--color-primary); color: var(--color-primary); background: color-mix(in srgb, var(--color-primary) 10%, transparent); }
-.status-badge.status-done { border-color: var(--color-success, #27ae60); color: var(--color-success, #27ae60); background: color-mix(in srgb, var(--color-success, #27ae60) 10%, transparent); }
+.status-badge.status-done { border-color: var(--color-success); color: var(--color-success); background: color-mix(in srgb, var(--color-success) 10%, transparent); }
 
 .btn-edit-task { margin-left: 0.25rem; }
 .btn-edit-task:hover { text-decoration: underline; }
@@ -614,7 +614,7 @@ defineExpose({ reload: loadAll });
   flex-shrink: 0;
 }
 .task-due.overdue {
-  color: var(--color-danger, #e74c3c);
+  color: var(--color-danger);
   font-weight: 500;
 }