Theme post code blocks + a11y fixes (impeccable audit) (#25)

Code blocks in posts rendered with the markdown plugin's default light highlight.js theme — white blocks on the dark ledger. This adds dark velvet pre/code styling and a Westgate-toned syntax palette (gold keywords, ledger-ink titles, muted green strings) for post content and the composer preview.

Also picks up the quick wins from an impeccable audit:

- Visible focus ring on the mobile drawer search (input had `outline: 0` with no replacement)
- Input placeholder contrast raised to pass WCAG 4.5:1; tagsinput placeholder reuses the token instead of `$gray-500`
- `prefers-reduced-motion` block zeroing transitions/animations (there were none before)
- Fixed a stray `</li>` closing a `<div>` in `quick-search-results.tpl`

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: #25
Co-authored-by: vickydotbat <vickydotbat@tutamail.com>
Co-committed-by: vickydotbat <vickydotbat@tutamail.com>

scss/overrides.scss

@@ -66,7 +66,7 @@ $input-bg: rgba($white, 0.025) !default;
 $input-color: $wg-text !default;
 $input-border-color: rgba($wg-gold, 0.18) !default;
 $input-focus-border-color: rgba($wg-gold, 0.42) !default;
-$input-placeholder-color: rgba($wg-text-soft, 0.62) !default;
+$input-placeholder-color: rgba($wg-text-soft, 0.74) !default;
 $btn-border-radius: 6px !default;
 $border-radius: 8px !default;
 $border-radius-sm: 6px !default;
@@ -109,5 +109,5 @@ $breadcrumb-active-color: $body-color !default;
 $breadcrumb-item-padding-x: 12px !default;
 
 .form-control::placeholder, .bootstrap-tagsinput::placeholder {
-	color: $gray-500 !important;
+	color: $input-placeholder-color !important;
 }