feat(desktop): auto-detect RTL/bidi text direction in chat

Arabic/Hebrew/Persian/Urdu chat text rendered left-to-right and
left-aligned, and mixed RTL/English technical messages (the common case)
read backwards. Resolve each chat block's base direction from its own
first strong character (UAX#9) with pure CSS, scoped to the chat
surfaces only:

- `unicode-bidi: plaintext` + `text-align: start` on assistant prose
  blocks (p, h1-h6, li, blockquote), the user bubble's text lines, and
  both composers (main + edit share the composer-rich-input slot). RTL
  blocks read and right-align RTL; English stays LTR; mixed
  conversations resolve per block. `text-align: start` is required
  because the user bubble hardcodes `text-left`.
- Inline `code` and KaTeX are pinned `direction: ltr; unicode-bidi:
  isolate`, so the bidi first-strong heuristic skips them: a sentence
  that *starts* with a command (`./run.sh ...`) followed by Arabic
  still resolves RTL, and the command's own neutrals keep their order.
- Fenced code surfaces (code-card, user fences) are pinned LTR so they
  never mirror or right-align inside an RTL list item or blockquote.

`direction` is never forced, so app chrome, layout, and list indent
stay LTR per the issue's request not to flip the whole UI. English-only
content is byte-for-byte unchanged.

Salvaged and unified from #44065 and #44169; verified in Chromium that
isolate removes inline code from the paragraph direction vote (the
code-first case), making the JS dir-resolution in #44065 unnecessary.

Fixes #44150

Co-authored-by: Adolanium <Adolanium@users.noreply.github.com>
Co-authored-by: Adalsteinn Helgason <AIalliAI@users.noreply.github.com>

apps/desktop/src/components/assistant-ui/user-message-text.tsx

@@ -127,7 +127,9 @@ const InlineSegmentView: FC<{ text: string }> = ({ text }) => {
   const nodes = useMemo(() => splitInlineCode(text), [text])
 
   return (
-    <span className="wrap-anywhere block whitespace-pre-line">
+    // styles.css bidi hook (#44150); whitespace-pre-line makes each line its own
+    // UAX#9 paragraph so it resolves direction independently.
+    <span className="wrap-anywhere block whitespace-pre-line" data-slot="aui_user-inline-text">
       {nodes.map((node, nodeIndex) =>
         node.kind === 'inline-code' ? (
           <code