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]>

snapshots/README.md

@@ -12,7 +12,7 @@ Raw pages, exactly as fetched. `scripts/refresh-sources.ts` writes them; nothing
 what those bytes are in — the `Content-Type` header, else a `<meta charset>` in the page, else
 UTF-8 — and `bytes` is the served length. A page in Shift_JIS or Latin-1 decoded as UTF-8 would be
 stored as a field of U+FFFD with the original bytes gone; re-parsing could never recover it, and the
-mojibake would reach `slugify`, moving every event ID for that source (CLAUDE.md § Event IDs are
+mojibake would reach `slugify`, moving every event ID for that source (AGENTS.md § Event IDs are
 localStorage keys).
 
 Every file is written to a sibling `.tmp-*` and renamed into place, body before metadata, so an
@@ -23,7 +23,7 @@ directory, so otherwise a run killed mid-write would pin a half-page in git fore
 Three reasons this is committed rather than cached:
 
 - **Re-parsing never re-fetches.** Iterating on a parser reads these files, not the wikis
-  (CLAUDE.md § Scraping conduct).
+  (AGENTS.md § Scraping conduct).
 - **A refresh is reviewable.** The commit diff is the page diff, so "an event vanished" is a
   question you can answer from git rather than from a wiki that has since changed again.
 - **The build stays offline.** `bun run build:feed` parses whichever of these exists and falls back