D6: AI Director polish + parity hardening

- pf2e parity: a unit test confirms the director carries the system through
  (systemConstraint + prompt say Pathfinder 2e, no cross-system leak) and still
  produces a grounded deterministic turn. (Degree-of-success/conditions already
  branch per system via the shared kernel.)
- UX: the transcript pane is now a bounded, scrollable region (max-h-[60vh]) so
  long sessions don't blow the page layout; it still auto-scrolls to the newest line.
- e2e: e2e/director.spec.ts exercises the full flow against a real browser — DM
  narrates a grounded scene with no API key (deterministic badge, empty-state
  clears, Continue appears), and the player persona seats a party character and
  takes a turn.

396 unit tests + 2 director e2e green; lint clean; build OK.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/features/assistant/director/TranscriptPane.tsx

@@ -18,7 +18,7 @@ export function TranscriptPane({ entries }: { entries: DirectorTranscriptEntry[]
   }
 
   return (
-    <div className="space-y-3">
+    <div className="max-h-[60vh] space-y-3 overflow-y-auto pr-1">
       {entries.map((e) => (
         <TranscriptLine key={e.id} entry={e} />
       ))}