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]>

src/ingest/robots.ts

@@ -2,7 +2,7 @@
  * robots.txt: parsing, matching, and a per-host cache.
  *
  * Sources are community wikis and this project's standing rule is to behave as
- * a guest would (CLAUDE.md § Scraping conduct). That starts with actually
+ * a guest would (AGENTS.md § Scraping conduct). That starts with actually
  * reading robots.txt rather than assuming a path is fair game.
  *
  * Parsing is a pure function over text, deliberately separated from fetching,