NPC editor, NPC tokens from library, admin management

- NPC library (own + shared) built on the character wizard with a free NPC preset
- NPC tokens in map editor and lobby, DM sheet on token click, DM checks for NPCs
- Admins can promote/demote other users

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HJhXuLD2Z6hv3Wqeq9UL9K

frontend/src/Presets.jsx

@@ -6,7 +6,7 @@ export default function Presets({ rules, reload }) {
   const [sel, setSel] = useState(rules.default_preset || 'standard')
   const [draft, setDraft] = useState(null) // preset being edited/created, null = viewing
   const [msg, setMsg] = useState('')
-  const presets = rules.presets || []
+  const presets = (rules.presets || []).filter((p) => !p.npc)
   const current = draft || presets.find((p) => p.id === sel) || presets[0]
   const editable = !!draft
   const own = !!current?.mine