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/phraser/phraser.go

@@ -1,9 +1,9 @@
 // Package phraser is maven's "rules decide, llm phrases" seam — the layer
 // that turns a loop decision into the body + summary the delivery module ships.
 //
-// Per DESIGN.md § Resident language model: the phraser is the resident model
+// Per docs/design.md § Resident language model: the phraser is the resident model
 // (Qwen3-1.7B — RU continued pretraining plus joint persona/router SFT, not a
-// sub-1b prompted-only model as the retired spec claimed; see DESIGN.md
+// sub-1b prompted-only model as the retired spec claimed; see docs/design.md
 // § Superseded, "small-model phrasing claim"). It takes
 // (rule, severity, context) and produces Body (full voice message, local — no
 // shoulder-surf concern beyond who's in the room) + Summary (minimal body for