docs: tier the tree by lifetime, so staleness shows in the path (V-446)

Seventeen markdown files at the repo root, twelve of them dated one-shot
reports sitting next to CLAUDE.md. That is why stale docs read as
current: nothing in the path said which was which.

Root now keeps CLAUDE.md and AGENTS.md. Living docs move under docs/
and carry a Last verified line. Dated measurements move to docs/evals/
ISO-prefixed, and are never edited after the day, so a newer number is
a new file. The senior review moves to docs/archive/.

Every reference was rewritten across markdown, Go comments, the Makefile
and the recall fixture. The touched Go packages still build.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/memory/recalleval/ru_recall_v1.json

@@ -41,7 +41,7 @@
       "tags": ["preference", "homelab", "paraphrase", "hard"],
       "query": "когда запускать резервное копирование",
       "want": "n1",
-      "note": "The DESIGN.md preference-seam example, phrased as the operator would ask it later.",
+      "note": "The docs/design.md preference-seam example, phrased as the operator would ask it later.",
       "notes": [
         {"id": "n1", "text": "бэкапы лучше делать ночью в три часа", "kind": "note"},
         {"id": "n2", "text": "обновления ставлю по субботам", "kind": "note"},