fix: replace rehype-pretty-code with react-syntax-highlighter for SSR compatibility

src/styles.css

@@ -282,65 +282,12 @@ a {
   }
 }
 
-/* ── Syntax Highlighting (rehype-pretty-code / Shiki) ─────────────────── */
-
-/* Code block wrapper */
-figure[data-rehype-pretty-code-figure] {
-  margin: 1.5rem 0;
-  border-radius: 0.75rem;
-  overflow: hidden;
-  border: 1px solid var(--line);
-}
-
-/* Title bar (e.g. ```ts filename.ts) */
-[data-rehype-pretty-code-title] {
-  background: var(--surface-strong);
-  color: var(--sea-ink-soft);
-  font-size: 0.75rem;
-  font-family: 'Manrope', sans-serif;
-  padding: 0.5rem 1rem;
-  border-bottom: 1px solid var(--line);
-  letter-spacing: 0.04em;
-}
-
-/* The <pre> block */
-pre[data-theme] {
-  background: var(--surface) !important;
-  padding: 1.25rem 1.5rem;
-  overflow-x: auto;
-  font-size: 0.875rem;
-  line-height: 1.7;
-}
-
-/* Inline code */
-:not(pre) > code[data-theme] {
+/* ── Inline code ──────────────────────────────────────────────────────── */
+.prose code:not([class]) {
   background: var(--chip-bg);
   border: 1px solid var(--chip-line);
   border-radius: 0.3rem;
   padding: 0.15em 0.45em;
   font-size: 0.85em;
-}
-
-/* Highlighted line */
-span[data-highlighted-line] {
-  background: color-mix(in oklch, var(--lagoon) 12%, transparent);
-  border-left: 2px solid var(--lagoon);
-  padding-left: calc(1.5rem - 2px);
-  margin-left: -1.5rem;
-  display: block;
-}
-
-/* Line numbers */
-code[data-line-numbers] {
-  counter-reset: line;
-}
-code[data-line-numbers] > [data-line]::before {
-  counter-increment: line;
-  content: counter(line);
-  display: inline-block;
-  width: 1rem;
-  margin-right: 1.5rem;
-  text-align: right;
-  color: var(--sea-ink-soft);
-  opacity: 0.4;
+  font-family: ui-monospace, monospace;
 }