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/adapters/index.ts

@@ -118,7 +118,7 @@ function toAdapter(spec: SourceSpec): Adapter {
       // keeps parsers what they are — pure readers of one site's markup.
       //
       // `sanitizeEvents` logs to console.warn by default, so a repaired or
-      // dropped event is never silent (CLAUDE.md § Silent drops).
+      // dropped event is never silent (AGENTS.md § Silent drops).
       return sanitizeEvents(parser.parse(html, ctx), {
         sourceId: ctx.sourceId,
         fallbackUrl: ctx.sourceUrl,