fix(desktop): tighten composer↔timeline parity for pre code and anchor

Address Marge's review on PR #913:

- pre code: add `block min-w-full whitespace-pre font-mono text-foreground`
  so pasted/markdown-rendered code blocks mirror CODE_BLOCK_CLASS in
  markdown.tsx token-for-token. Previously the composer's pre code only
  reset the inline-code styling; it inherited block layout by default,
  which is fine in practice but isn't true parity.
- anchor: add `transition-colors hover:text-primary/80` so hover
  treatment matches the rendered timeline.

Heading sizes, pre shadow (shadow-xs), and pre max-h ([400px]) were
flagged in review but already match markdown.tsx exactly (h1=text-xl
leading-8, h2=text-lg leading-7, h3=text-base leading-6 at line 791-806;
pre uses shadow-xs and max-h-[400px] at line 436). No change needed
there.

Verified: pnpm typecheck, pnpm lint, pnpm build all green.

desktop/src/shared/styles/globals.css

@@ -316,7 +316,7 @@
   text-decoration: line-through;
 }
 .rich-text-composer .tiptap a {
-  @apply font-medium text-primary underline underline-offset-4 cursor-pointer;
+  @apply font-medium text-primary underline underline-offset-4 transition-colors hover:text-primary/80 cursor-pointer;
 }
 
 /* Inline code. */
@@ -329,7 +329,9 @@
   @apply max-h-[400px] overflow-x-auto overflow-y-auto rounded-xl border border-border/70 bg-muted/60 px-3 py-1.5 shadow-xs;
 }
 .rich-text-composer .tiptap pre code {
-  @apply bg-transparent p-0 rounded-none text-[13px] leading-6;
+  /* Mirrors CODE_BLOCK_CLASS in markdown.tsx so a pasted/markdown-rendered
+   * code block looks identical in the composer and in the timeline. */
+  @apply block min-w-full whitespace-pre rounded-none bg-transparent p-0 font-mono text-[13px] leading-6 text-foreground;
 }
 
 /* Blockquote. */