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/rules_test.go

@@ -18,7 +18,7 @@ import (
 //   - does it stay quiet when it should?
 //   - is it silent when the key it needs has no data at all?
 //
-// The last one is load-bearing. DESIGN.md: "since(key)==null → don't fire.
+// The last one is load-bearing. docs/design.md: "since(key)==null → don't fire.
 // Silence on no-data is 'shuts up when uncertain'."
 
 // stateWith builds a snapshot at refTime() holding just the given facts.
@@ -179,7 +179,7 @@ func TestCareRulePredicates(t *testing.T) {
 
 // ---------------------------- ops rules --------------------------------------
 
-// The two ops rules match on a value AND on which poller wrote it. DESIGN.md:
+// The two ops rules match on a value AND on which poller wrote it. docs/design.md:
 // "a compromised poller must not be able to forge a trigger." Half of this
 // table is forgery attempts; all of them must be refused.
 func TestOpsRulePredicates(t *testing.T) {
@@ -331,7 +331,7 @@ func TestNoDefaultRuleFiresOnEmptyState(t *testing.T) {
 	}
 }
 
-// Severities are the delivery contract (DESIGN.md § Delivery / channel
+// Severities are the delivery contract (docs/design.md § Delivery / channel
 // routing): care is sev1-2 and drops when away, ops is sev3-4 and holds. Pin
 // them so a change to a rule's insistence has to be deliberate.
 func TestDefaultRuleSeverities(t *testing.T) {
@@ -356,7 +356,7 @@ func TestDefaultRuleSeverities(t *testing.T) {
 	}
 }
 
-// Cooldown bounds keep the feedback tuner honest — DESIGN.md wants
+// Cooldown bounds keep the feedback tuner honest — docs/design.md wants
 // `cooldown in [min,max]` "so a weird week can't mutate Maven silent or
 // stalker". A base outside its own envelope would make that meaningless.
 func TestDefaultRuleCooldownsAreBounded(t *testing.T) {