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/SettingsView.vue

@@ -2789,11 +2789,11 @@ function formatUserDate(iso: string): string {
   color: var(--color-text-muted);
 }
 .perm-granted { background: color-mix(in srgb, var(--color-success) 15%, transparent); color: var(--color-success); }
-.perm-denied  { background: color-mix(in srgb, var(--color-danger, #e74c3c) 15%, transparent); color: var(--color-danger, #e74c3c); }
+.perm-denied  { background: color-mix(in srgb, var(--color-danger) 15%, transparent); color: var(--color-danger); }
 .sub-active   { background: color-mix(in srgb, var(--color-success) 15%, transparent); color: var(--color-success); }
 .push-error {
   font-size: 0.82rem;
-  color: var(--color-danger, #e74c3c);
+  color: var(--color-danger);
   margin: 0.25rem 0 0;
 }
 
@@ -3048,7 +3048,7 @@ function formatUserDate(iso: string): string {
 
 .group-card {
   border: 1px solid var(--color-border);
-  border-radius: var(--radius-md, 8px);
+  border-radius: var(--radius-md);
   overflow: hidden;
 }
 
@@ -3166,7 +3166,7 @@ function formatUserDate(iso: string): string {
   padding: 0.15rem 0.4rem;
   border-radius: 4px;
 }
-.role-owner { background: color-mix(in srgb, var(--color-warning, #f59e0b) 15%, transparent); color: var(--color-warning, #f59e0b); }
+.role-owner { background: color-mix(in srgb, var(--color-warning) 15%, transparent); color: var(--color-warning); }
 .role-member { background: color-mix(in srgb, var(--color-muted) 15%, transparent); color: var(--color-muted); }
 
 .members-empty {
@@ -3278,7 +3278,7 @@ function formatUserDate(iso: string): string {
 }
 .api-key-value {
   flex: 1;
-  background: var(--color-surface-2, var(--color-surface));
+  background: var(--color-surface-2);
   padding: 0.4rem 0.6rem;
   border-radius: var(--radius-sm);
   font-size: 0.85rem;
@@ -3396,7 +3396,7 @@ function formatUserDate(iso: string): string {
 .mcp-code-row .btn-sm { white-space: nowrap; }
 .mcp-advanced {
   margin-top: 1.25rem;
-  border-top: 1px solid var(--color-border, rgba(255, 255, 255, 0.1));
+  border-top: 1px solid var(--color-border);
   padding-top: 0.75rem;
 }
 .mcp-advanced summary {
@@ -3470,7 +3470,7 @@ function formatUserDate(iso: string): string {
   flex: 1;
 }
 .voice-library-id {
-  font-family: var(--font-mono, monospace);
+  font-family: var(--font-mono);
   font-size: 0.9rem;
   font-weight: 500;
 }
@@ -3511,9 +3511,9 @@ function formatUserDate(iso: string): string {
   border-radius: 999px;
 }
 .status-on {
-  background: color-mix(in srgb, var(--color-success, #22c55e) 15%, transparent);
-  color: var(--color-success, #22c55e);
-  border: 1px solid color-mix(in srgb, var(--color-success, #22c55e) 40%, transparent);
+  background: color-mix(in srgb, var(--color-success) 15%, transparent);
+  color: var(--color-success);
+  border: 1px solid color-mix(in srgb, var(--color-success) 40%, transparent);
 }
 .status-off {
   background: color-mix(in srgb, var(--color-text-muted) 10%, transparent);