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

crates/cph-diag/src/lib.rs

@@ -2,7 +2,7 @@
 //!
 //! Every other crate in the workspace depends on these types to report
 //! problems. The vocabulary is intentionally small and stable: a [`Severity`]
-//! (mirroring the Lean master), a closed set of machine-stable [`DiagCode`]s, an
+//! (two-valued, ADR-0010), a closed set of machine-stable [`DiagCode`]s, an
 //! optional [`SourceSpan`] pointing back at the offending source, and a
 //! [`Diagnostic`] tying them together with a human message and a fix hint.
 //!
@@ -17,32 +17,27 @@ use serde::Serialize;
 
 /// Severity of a diagnostic.
 ///
-/// **Mirrors `Spec.Courseware.Diagnostic.Severity`** in the Lean semantic
-/// master (`spec/Spec/Courseware/Check/Diagnostic.lean`), whose definition is
-/// exactly:
+/// **Pinned by ADR-0005 / ADR-0010: exactly two values.**
 ///
 /// ```text
-/// inductive Severity where
-///   | warning
-///   | error
+/// warning | error
 /// ```
 ///
-/// This two-valued shape is a **contract decision**, not an accident: the Lean
-/// module pins `Severity` to exactly `warning | error` and states the finer
-/// levels (`info` / `hint` / `note`) are deliberately undecided. We therefore
+/// This two-valued shape is a **contract decision**, not an accident: the
+/// finer levels (`info` / `hint` / `note`) are deliberately undecided, so we
 /// do **not** add an info/note level here. `error` blocks (the artifact is
 /// invalid); `warning` does not block (the artifact still exports, but with
 /// loss / an ignored element — e.g. ADR-0005's "missing render ⇒ warning").
 ///
-/// There is no CI gate enforcing this alignment (see the repo constitution);
-/// it is maintained by review, which is why this correspondence is documented
-/// here rather than only in the spec.
+/// There is no CI gate enforcing ADR↔implementation alignment (see the repo
+/// constitution); it is maintained by review, which is why the decision is
+/// documented here rather than only in the ADR.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize)]
 pub enum Severity {
     /// Non-blocking: the artifact still exports, but is lossy / has an ignored
-    /// element. Mirrors Lean `Severity.warning`.
+    /// element. ADR-0010 `warning`.
     Warning,
-    /// Blocking: the artifact is invalid. Mirrors Lean `Severity.error`.
+    /// Blocking: the artifact is invalid. ADR-0010 `error`.
     Error,
 }