Add Phase 12: native RPG world state

Structured world/player/NPC stats, two-way flags, and sticky milestones
per scenario (stat_schema). The AI proposes a per-turn delta; a Python
engine referees it (clamp to min/max, per-turn cap, cooldown, counters).
Band word-labels plus a fixed stat guide (descriptions + full ranges)
keep the model grounded. World State drawer + Insights delta report;
undo/retry roll it back via the Phase 11 snapshot pattern.

- migrations 26-28 (scenarios.stat_schema, adventures.world_state,
  actions.world_state_before); all nullable, additive, safe on existing rows
- migration 29 raises the default context budget 4096 -> 16384
  (custom values preserved)
- seeded demo scenario 04-rpg-world-state.json (Bandit Camp)
- 19 new tests (33 total pass)

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

frontend/src/api.js

@@ -80,6 +80,7 @@ export const api = {
   listAdventures: () => request('/adventures'),
   getAdventure: (id) => request(`/adventures/${id}`),
   getScriptState: (id) => request(`/adventures/${id}/script-state`),
+  getWorldState: (id) => request(`/adventures/${id}/world-state`),
   createAdventure: (data) => request('/adventures', { method: 'POST', body: JSON.stringify(data) }),
   updateAdventure: (id, data) => request(`/adventures/${id}`, { method: 'PATCH', body: JSON.stringify(data) }),
   deleteAdventure: (id) => request(`/adventures/${id}`, { method: 'DELETE' }),