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/origins/README.md

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+# /content/origins — starting-state seeds
+
+Thin authored files, one per starting point. An origin is an **initial-state
+overlay** on the static shared world (`/content/world`): where the player begins,
+the opening situation, and seeds for dispositions, inventory, starting quest, and
+character-creation constraints. Values and id references — never maps or personas.
+
+At new-game the player picks an origin; code constructs the runtime canon log
+from origin + world content + character creation. See the spec in
+[`/docs/canon-log.md`](../../docs) (design under
+[`/docs/superpowers/specs`](../../docs/superpowers/specs)).
+
+## Scope (§17)
+
+Schema supports **N** origins; the POC authors **one**. One world, one map, fixed
+NPCs — origins change only the player's starting point and situation. More
+replayability, flat authoring cost.
+
+## Fields (summary)
+
+`id` · `display_name` · `description` · `start_location_id` · `situation[]` ·
+`opening_facts[]` · `disposition_overrides{}` · `inventory_grants[]` ·
+`start_quest_id` · `build_constraints{}`
+
+`humiliations` are never seeded — they are earned in play (§7/§9). Validated
+against `origin.schema.json`; every id must resolve in `/content/world`.