chore: remove Lean spec; ADRs are the single source of truth

The spec/ Lean semantic master had no conformance gate, no codegen, and
no CI tie to implementations — alignment was carried entirely by human
review, the same mechanism that carries the ADRs. In practice the ADRs
plus greppable code comments were already the load-bearing artifacts,
so spec/ was the most expensive kind of stale documentation.

- delete spec/ and the spec-check CI workflow
- README: constitution rewritten around ADRs as decision truth
- AGENTS.md/CLAUDE.md: discipline re-anchored (new decisions -> new ADR,
  never rewrite ADR history; supersede instead)
- code comments: re-anchor 'Mirrors Spec.X' invariants to ADR numbers
  (cph-diag, cph-check, cph-model, hub runner/capacity/org, prisma)
- leave ADR bodies and .scratch audit snapshots untouched (history);
  fix live references in open readiness tickets

.scratch/saas-production-readiness/issues/05-define-abuse-capacity-controls.md

@@ -29,7 +29,7 @@ workload brakes.
 
 The full current-state inventory, accepted behavior, and release evidence are
 recorded in [Initial abuse and capacity controls](../assets/initial-abuse-capacity-controls.md),
-with the durable decision in ADR-0022 and `Spec.System.Capacity`. Numerical
+with the durable decision in ADR-0022. Numerical
 ceilings remain open until production-like calibration.
 
 The implementation frontier is:

.scratch/saas-production-readiness/issues/08-prove-production-release-gate.md

@@ -7,6 +7,6 @@ Blocked by: 01, 02, 03, 04, 05, 06, 07, 09, 10, 11, 12, 13, 14, 15, 16, 17, 18,
 ## Question
 
 After the readiness investigations and resulting fixes are resolved, can one
-repeatable release procedure prove build/test/spec health, deploy a clean
+repeatable release procedure prove build/test health, deploy a clean
 production-like environment, exercise critical tenant and agent journeys,
 verify observability and recovery, and either roll forward or roll back safely?

.scratch/saas-production-readiness/issues/27-reconcile-audit-history-contract.md

@@ -8,7 +8,7 @@ Blocked by: 04
 
 Separate or unify run-bound audit entries, pre-run security/permission events,
 structured messages, and operational recovery events without weakening
-`Spec.System.Audit`'s pinned AuditEntry-to-run relation. Decide durability,
+the pinned AuditEntry-to-run relation. Decide durability,
 failure, retention, and query semantics; then enforce referential integrity and
 observable/recoverable writes instead of silently swallowing lost evidence.
 Do not merge these customer Project/Run records with ADR-0023's already-decided

.scratch/saas-production-readiness/issues/42-decide-platform-admin-identity-audit.md

@@ -40,9 +40,7 @@ an off-host recovery key, an incident and reason, and issues only an expiring
 Emergency Platform Grant.
 
 The complete accepted decision and implementation divergences are in
-[ADR-0023](../../../docs/adr/0023-platform-administrator-identity-and-audit.md).
-The pinned semantic invariants are in
-[`Spec.System.PlatformAdministration`](../../../spec/Spec/System/PlatformAdministration.lean),
+[ADR-0023](../../../docs/adr/0023-platform-administrator-identity-and-audit.md),
 and the canonical terms are in [`CONTEXT.md`](../../../CONTEXT.md).
 
 Exact numeric session/invitation/step-up limits and browser mechanics remain