docs: move the working agreement to AGENTS.md

The guidance in here is not Claude-specific — it is what this project is,
what it refuses to do, and the rules that are invisible from the code. Any
agent working here needs it, and AGENTS.md is the name they all look for.

CLAUDE.md stays as a pointer so Claude Code still finds it, and holds no
guidance of its own; two copies would drift and the wrong one would be read.
Every cross-reference in the source comments, docs, workflow and skills now
names AGENTS.md, and the image ignores both.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

.claude/agents/adapter-author.md

@@ -44,7 +44,7 @@ source (wiki.gg) turned out to publish ISO timestamps with per-region timers.
   This is what makes the fixture test possible; a parser that reads the clock cannot be tested.
 - Implement `canParse` as a *structural* check, and do not over-fit it. Game8's own pages differ in
   attribute quote style, so `class="a-table"` would falsely reject half of them.
-- Get the domain rules right — they are in `CLAUDE.md` § Domain rules and they are where adapters
+- Get the domain rules right — they are in `AGENTS.md` § Domain rules and they are where adapters
   actually go wrong:
   - All timestamps UTC ISO 8601.
   - Banners are usually global (`regionScoped: false`); story/login events usually follow per-region

.claude/skills/add-game-source/SKILL.md

@@ -55,7 +55,7 @@ requirements are the same:
   sources are a single entry in `SOURCES`, with no new parsing code.
 - Source-timezone → UTC, region offsets, and ID construction happen in the parser's event builder.
 
-**The three domain rules that break new adapters**, from `CLAUDE.md`:
+**The three domain rules that break new adapters**, from `AGENTS.md`:
 
 1. Everything stored as UTC ISO 8601.
 2. Banners are usually one global end instant; story and login events usually end at each region's