Add free-text stat type to the world-state RPG layer

Numeric stats couldn't represent things like worn armor or held items.
A stat can now be marked type: "text" — the AI reports the new full
value instead of a delta, with no clamping/bands (cooldown still
applies). Updated the scenario editor's stat kind selector, the
World State drawer's stat display, and the emit-rule prompt; added
tests and an outfit stat to the RPG demo scenario.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/app/seed_data/04-rpg-world-state.json

@@ -21,6 +21,10 @@
         "desc": "Magical energy for spells; spent casting, restored by resting.",
         "min": 0, "max": 50, "initial": 30, "max_delta_per_turn": 25,
         "bands": [[0, 10, "drained"], [10, 30, "steady"], [30, 51, "brimming"]]
+      },
+      "outfit": {
+        "type": "text", "initial": "worn leather armor, travel-stained",
+        "desc": "What the player is currently wearing/carrying visibly; update it when gear is gained, lost, or changed."
       }
     },
     "flags": {