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/tool/tool.go

@@ -2,7 +2,7 @@
 // store's allowlist, and drafts 'proposed' scaffolds for acts that aren't on
 // it yet.
 //
-// Boundary discipline (DESIGN.md § "Tool registration — drafting is suggest,
+// Boundary discipline (docs/design.md § "Tool registration — drafting is suggest,
 // enabling is act"):
 //
 //   - The store is the allowlist. Only status='enabled' rows run. A verb not
@@ -26,7 +26,7 @@
 //   - Destructive tools don't run on first hearing: Exec returns ErrNeedsConfirm
 //     and the handler runs a confirm turn ("выполнить X? да/нет"); only a
 //     confirmed re-Exec runs them. A gate assumes a fully-formed action, which
-//     an enabled+matched act is (DESIGN.md § "Confirmation is not one
+//     an enabled+matched act is (docs/design.md § "Confirmation is not one
 //     mechanism").
 package tool