Keep agent guidance in one root AGENTS.md (closes #31)

The canonical REPO_POLICIES.md now says that guidance for coding agents lives in one AGENTS.md at the repository root, including anything an agent should remember between sessions, and is never committed under a file or directory named after one agent tool or split into separate memory files. This retires the in-repo memory rule that older vendored copies still carry.

AGENTS.md is added to the list of files allowed in the root, which would otherwise contradict the new rule. Both checklists carry the matching item.

Model: opus-5-5

TODO.md

@@ -21,6 +21,12 @@ fmt-check, and commit.
 
 # Completed Steps
 
+- 2026-10-04: `REPO_POLICIES.md` now states that guidance for coding agents
+  lives in one `AGENTS.md` at the repository root, never under a file or
+  directory named after one agent tool and never in separate memory files (issue
+  31). This retires the rule, still present in older vendored copies, that kept
+  agent memory as committed files under `.claude/memory/`. `AGENTS.md` joins the
+  list of files allowed in the root, and both checklists say so.
 - 2026-10-04: The Makefile examples in the Go styleguide and the HTTP server
   conventions now fall back to `dev` when `git describe` prints nothing (outside
   a git checkout, or where git is missing or refuses the checkout), instead of