docs: canon log schema + origin seed design

Design spec for the §11 canon log, plus origin seeds as thin initial-state
overlays over a single static world. Three layers (world content / origin seed /
runtime canon log), the in/out boundary (numeric Luck never enters the AI
payload, §7), field-level schemas, new-game construction order, turn-to-turn
maintenance, and JSON storage validated on both client and api.

Folds content/npcs and content/quests under content/world/; adds
content/world/{locations,items} and content/origins. fallback/ kept outside
world/ (authored prose, not id-referenced).

Spec: docs/superpowers/specs/2026-07-09-canon-log-schema-design.md

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

content/world/locations/README.md

@@ -0,0 +1,8 @@
+# /content/world/locations
+
+The map — towns, dungeons, points of interest, each with a stable **id**. An
+origin's `start_location_id` resolves here; the canon log's `location` mirrors
+the current one (id + display name).
+
+POC scope (§17): one town, one dungeon (three fights, one boss). One reusable
+world; origins vary only where the player begins within it.