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

hub/src/org/capacityPolicy.ts

@@ -1,9 +1,9 @@
 /**
- * Org capacity policy service (ADR-0022 / spec `Spec.System.Capacity`).
+ * Org capacity policy service (ADR-0022).
  *
  * Stores per-Organization lower `organizationLimit` overrides per
- * `CapacityDimension`. Enforces `LayeredLimit.Valid`: a set limit must be ≤ the
- * platform ceiling for that dimension. `LayeredLimit.effective` (min of the two)
+ * `CapacityDimension`. Enforces the layered-limit invariant: a set limit must be ≤ the
+ * platform ceiling for that dimension. The effective limit (min of the two)
  * is the value capacity admission should use; dimensions with no org override
  * fall back to the platform ceiling.
  */