feat(UI): hide NPC/monster HP toggle (player display)

Mirrors hidePlayerHp. New hideNpcHp flag on activeDisplay doc.
- AdminView: 'Hide NPC/monster HP' switch in Player Display settings.
- DisplayView: HP bar gated by !(hideNpcHp && p.type !== 'character').
  Covers monsters + NPCs (all non-player).
- Default false (show NPC HP) — opposite of player HP default true.

updateDoc patch (BUG-4 pattern). No clobber.

Test: HideHpToggle selector scoped to 'hide player hp' (now 2 switches).

src/tests/HideHpToggle.test.js

@@ -43,7 +43,7 @@ describe('BUG-4: hide-player-HP toggle preserves activeDisplay', () => {
     await selectCampaignByName('Camp');
 
     // find the hide-player-HP toggle (role switch)
-    const toggle = await screen.findByRole('switch', { name: /hide/i }, { timeout: 3000 });
+    const toggle = await screen.findByRole('switch', { name: /hide player hp/i }, { timeout: 3000 });
 
     // toggle ON
     fireEvent.click(toggle);