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/llmphraser.go

@@ -692,7 +692,7 @@ func (p *LLMPhraser) chatWithSystem(ctx context.Context, system, user string, ma
 // Written as filled-in examples, not as a schema with "..." in it. A 0.8B
 // copies whatever sits in the response slot, so a literal placeholder there
 // teaches it to answer with the placeholder. Measured: 7/15 nudges came back
-// as "..." before this. See PHRASING-EVAL-31-07-2026.md.
+// as "..." before this. See docs/evals/2026-07-31-phrasing.md.
 //
 // Russian only, feminine self-reference, second person masculine (the owner is
 // a man). She talks TO him, informally, singular — never "вы", never "он".