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/rules/RulebookDetailPane.vue

@@ -122,7 +122,7 @@ watch(() => props.rulebookId, () => {/* re-render of isSubscribed from existing
 </template>
 
 <style scoped>
-.pane { background: var(--color-surface, #18181b); padding: 1rem; overflow-y: auto; }
+.pane { background: var(--color-surface); padding: 1rem; overflow-y: auto; }
 header { display: flex; align-items: center; justify-content: space-between; gap: 1rem; }
 header h2 { font-family: Fraunces, serif; font-style: italic; margin: 0 0 0.5rem 0; }
 .always-on-toggle {
@@ -133,18 +133,18 @@ header h2 { font-family: Fraunces, serif; font-style: italic; margin: 0 0 0.5rem
 .always-on-toggle input { cursor: pointer; }
 ul { list-style: none; padding: 0; margin: 1rem 0; }
 li { padding: 0.5rem; cursor: pointer; border-radius: 6px; }
-li.active { background: var(--color-primary-bg, rgba(99,102,241,0.15)); }
-li:hover { background: var(--color-hover, rgba(255,255,255,0.05)); }
+li.active { background: var(--color-primary-bg); }
+li:hover { background: var(--color-hover); }
 .new-topic input {
   width: 100%; margin-bottom: 0.5rem;
-  background: var(--color-bg, #111113); color: inherit;
-  border: 1px solid var(--color-border, #2a2a2e); border-radius: 6px;
+  background: var(--color-bg); color: inherit;
+  border: 1px solid var(--color-border); border-radius: 6px;
   padding: 0.5rem;
 }
 .form-buttons { display: flex; gap: 0.5rem; }
 .subscriptions {
   margin-top: 2rem;
-  border-top: 1px solid var(--color-border, #2a2a2e);
+  border-top: 1px solid var(--color-border);
   padding-top: 1rem;
 }
 .subscriptions h3 { font-size: 0.9em; opacity: 0.7; text-transform: uppercase; letter-spacing: 0.05em; }