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/loop/gate_test.go

@@ -10,12 +10,12 @@ import (
 
 // Tests for the universal restraint gate.
 //
-// DESIGN.md § Trigger model: "the gate is universal, applied by the loop, never
+// docs/design.md § Trigger model: "the gate is universal, applied by the loop, never
 // per-rule — quiet-hours, presence, cooldown, snooze, calendar-busy all live in
 // one fires()." These tests pin the CONSERVATIVE side of that: the cases where
 // Maven must stay quiet. They exist so nobody loosens the gate by accident.
 //
-// Where the code does not yet do what DESIGN.md promises, the test is written to
+// Where the code does not yet do what docs/design.md promises, the test is written to
 // show the gap and then skipped, with the file and line to fix. Behaviour is not
 // changed to make a test pass.
 
@@ -54,7 +54,7 @@ func TestGateQuietHoursSuppressesCareOnly(t *testing.T) {
 
 // ---------------------------- presence ---------------------------------------
 
-// DESIGN.md § Delivery: "sev <= 2 drops on away, sev >= 3 holds: a missed water
+// docs/design.md § Delivery: "sev <= 2 drops on away, sev >= 3 holds: a missed water
 // nudge is noise, a missed backup failure isn't."
 func TestGateAwayDropsCareHoldsOps(t *testing.T) {
 	cases := []struct {
@@ -250,7 +250,7 @@ func TestTickOrderOfRulesDoesNotMatter(t *testing.T) {
 
 // ---------------------------- reminders bypass the gate ----------------------
 
-// DESIGN.md § User reminders: "bypasses the restraint gate — 'wake me 7' fires
+// docs/design.md § User reminders: "bypasses the restraint gate — 'wake me 7' fires
 // in quiet hours; that's the point." Every suppressor set at once, and the
 // reminder still comes through.
 func TestRemindersBypassEverySuppressor(t *testing.T) {
@@ -269,7 +269,7 @@ func TestRemindersBypassEverySuppressor(t *testing.T) {
 	}
 }
 
-// GAP — DESIGN.md § User reminders ends "Snooze still applies." RemindDecisions
+// GAP — docs/design.md § User reminders ends "Snooze still applies." RemindDecisions
 // passes every due reminder straight through with no snooze check, so a snoozed
 // reminder fires anyway. The test below is what the contract asks for.
 func TestRemindersStillHonourSnooze(t *testing.T) {