Phase 6: character creation & level-up

- Ability generation: standard array, point buy (27-pt, validated), 4d6kh3 roll;
  AbilityGenModal with assign-from-pool + steppers (pure abilityGen lib + tests)
- Level-up flow: increment level, HP gain (average or roll hit die + CON)
- Print / save-to-PDF: print button + @media print hides app chrome and roll tray
- Plan: added Phase 11 (data-driven Assistant) to the roadmap

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/components/ui/RollTray.tsx

@@ -9,7 +9,7 @@ export function RollTray() {
   if (!last) return null;
 
   return (
-    <div className="pointer-events-none fixed bottom-4 right-4 z-50 w-72">
+    <div data-roll-tray className="pointer-events-none fixed bottom-4 right-4 z-50 w-72 print:hidden">
       <div
         key={last.seq}
         className="animate-dice-settle pointer-events-auto rounded-lg border border-line bg-panel p-4 shadow-2xl"