Make NPCs a dedicated section with per-NPC stats

Replace the single shared `npc` stat template (+ npc_card_types) with an
`npcs` section: each NPC keyed by a stable id, carrying its own name,
description, trigger keys, and its OWN stats block. The AI addresses NPCs
as npc.<id>.<stat> (id shown in context), which also fixes the old
card-id-guessing problem. On adventure creation each NPC auto-creates a
story card (name/keys/desc) for lore + in-scene detection, unless a
same-name card already exists. All NPCs instantiate up front.

- engine: npcs instantiate/apply/render/reference, npc_name/npc_triggers
- builder: _visible_npcs matches each NPC's own keys
- create_adventure: auto-create story cards from npcs
- WorldStateDrawer: render defined NPCs with their own stats + desc tooltip
- demo seed: Gwen (health/trust) + Bandit Leader (health/aggression)
- tests updated (34 pass); no new migration (npcs lives in stat_schema JSON)

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

backend/app/routers/adventures.py

@@ -98,6 +98,7 @@ def create_adventure(
     db.flush()
 
     if scenario:
+        existing_names = {(c.name or "").strip().lower() for c in scenario.story_cards}
         for card in scenario.story_cards:
             db.add(
                 models.StoryCard(
@@ -109,6 +110,24 @@ def create_adventure(
                     notes=card.notes,
                 )
             )
+        # Phase 12: each defined NPC gets a story card (for its description as
+        # lore + in-scene triggering), unless a card with that name already exists.
+        for npc_key, ndef in (scenario.stat_schema or {}).get("npcs", {}).items():
+            if not isinstance(ndef, dict):
+                continue
+            name = worldstate.npc_name(ndef, npc_key)
+            if name.strip().lower() in existing_names:
+                continue
+            db.add(
+                models.StoryCard(
+                    adventure_id=adventure.id,
+                    type="character",
+                    name=name,
+                    keys=fill_placeholders(str(ndef.get("keys") or name), values),
+                    entry=fill_placeholders(str(ndef.get("desc") or ""), values),
+                    notes="",
+                )
+            )
         for position, script in enumerate(scenario.scripts):
             db.add(
                 models.AdventureScript(