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

backend/data/rules.json

@@ -31,6 +31,7 @@
     {"id": "standard", "name": "Standard", "desc": "The numbers from the brainstorm document.", "creation": {}},
     {"id": "gritty", "name": "Gritty survival", "desc": "Example preset: fewer points, one starting talent, harder to learn advanced skills.", "creation": {"attr_points": 70, "skill_points_default": 100, "talents_max": 1, "free_proficiencies": 1, "advanced_unlock_cost": 15}},
     {"id": "heroic", "name": "Heroic", "desc": "Example preset: more points, higher attribute cap, three starting talents.", "creation": {"attr_points": 110, "attr_max_raise": 25, "attr_max": 50, "skill_points_default": 200, "talents_max": 3, "free_proficiencies": 3, "advanced_unlock_cost": 5}},
+    {"id": "npc", "name": "NPC / creature (free)", "desc": "Used by the NPC editor: huge pools, no limits.", "npc": true, "creation": {"attr_points": 500, "attr_max_raise": 100, "attr_max": 150, "skill_points_default": 1000, "talents_min": 0, "talents_max": 10, "free_proficiencies": 20, "advanced_unlock_cost": 0}},
     {"id": "oneshot", "name": "One-shot", "desc": "Example preset: quick, strong characters for a single session.", "creation": {"attr_points": 100, "skill_points_default": 120, "talents_max": 2, "free_proficiencies": 3, "advanced_unlock_cost": 0}}
   ],