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>

maven-feature-ranking.md

@@ -1,6 +1,6 @@
 # maven — feature ranking
 
-> dated 2026-07-03. companion to `DESIGN.md` (folded from the former `maven.md`). ranks everything discussed post-repo-state against the infra blockers, not a replacement for the build order.
+> dated 2026-07-03. companion to `docs/design.md` (folded from the former `maven.md`). ranks everything discussed post-repo-state against the infra blockers, not a replacement for the build order.
 
 ---
 
@@ -20,7 +20,7 @@ nothing feature-level below should land before 1–2 are done. 3–4 can interle
 ### mandatory
 things that block correctness or safety of stuff already shipped — not new capability, just closing gaps in existing design.
 
-- **destructive-confirm policy** — open question in `DESIGN.md` § open questions, blocks correx and any new tool domain from having a coherent risk tier
+- **destructive-confirm policy** — open question in `docs/design.md` § open questions, blocks correx and any new tool domain from having a coherent risk tier
 - **quiet-hours definition** — open question, blocks proactive delivery being trustworthy
 - **schema migrations** — sqlcipher rollout alone forces a schema touch. want this mechanism before that, not after.
 
@@ -30,7 +30,7 @@ cheap, no dependencies, no new invariants.
 - **grocery / `list_items` table** — fourth append-only shape (item, status, list-tag), no predicate touches it, multi-adder just works for free
 - **go.mod tidy**
 - **capability model** (deepseek) — `homelab.docker.restart` instead of flat `tool→enabled`. cheap now, expensive to retrofit once tools surface passes ~15 entries. time-sensitive, not urgent.
-- **conversation repair** — already free: `DESIGN.md` has "misroute correction = new centroid example," this is just naming the existing mechanism as a feature
+- **conversation repair** — already free: `docs/design.md` has "misroute correction = new centroid example," this is just naming the existing mechanism as a feature
 - **command history** — read-only query over existing facts, no new mechanism
 - **clarification templates** — canned phrasing for the router's existing confidence-gate fallback, phraser-lane only
 - **pronunciation dictionary** — tts config, no architecture