Inventory polish: smaller phone/notebook, phone higher, auto-open, exit to board

The phone and notebook render a bit smaller; the phone sits higher on screen;
in-game the handset opens automatically (session mode); and the tool view
gains an EXIT ✕ that closes the inventory straight back to the board.

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

src/inventory.tsx

@@ -91,6 +91,7 @@ export function Inventory({ onClose, session, onTearToBoard }: { onClose?: () =>
 
   if (active) return <div className="inv-tool">
     <button className="inv-back" onClick={() => setActive(null)}>‹ TOOLS</button>
+    {onClose && <button className="inv-exit" onClick={onClose}>EXIT ✕</button>}
     {active === 'phone' ? <PhonePreview session={session} /> : <NotebookTool playthroughId={session?.playthroughId} onTear={onTearToBoard} />}
   </div>