ECOSYSTEM: record proven-tests-and-benches as the test framework (#178)

## Context

`proven-tests-and-benches` now grades proven's modules by three-tier
provenance (Actually-/Provisionally-/Unproven), reading proven's own
`MODULE-STATUS.txt` + `.machine_readable/6a2/STATE.a2ml` OWED ledger —
without re-checking proofs. The two repos previously had **zero
references in either direction**. This adds the reciprocal link so the
ecosystem manifest is accurate.

## Change

One file: `.machine_readable/6a2/ECOSYSTEM.a2ml` gains a `[relations]`
entry pointing at proven-tests-and-benches, noting that its as-declared
reading (4/37/47) reconciles with `MODULE-STATUS.txt` while the strict
evidence-carrying reading reports 0 Actually-Proven (the 4 proof-bearing
modules all carry OWED axioms). No source or proof changes.

## Verification

Documentation-only; no build impact. The grading it references is
reproducible from the proven-tests-and-benches PR: `PROVEN_ROOT=<this
checkout> proven-subject-report`.

Related: `hyperpolymath/proven-tests-and-benches#13`.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01SW76f8XBgwsiGXU9x5vmQU

---
_Generated by [Claude
Code](https://claude.ai/code/session_01SW76f8XBgwsiGXU9x5vmQU)_

Co-authored-by: Claude <noreply@anthropic.com>

Author: hyperpolymath

.machine_readable/6a2/ECOSYSTEM.a2ml

@@ -8,3 +8,8 @@ ecosystem = "hyperpolymath"
 
 [position]
 type = "component"
+
+[relations]
+relations = [
+  { project = "proven-tests-and-benches", relation = "test-framework", detail = "grades proven's modules by three-tier provenance (Actually-/Provisionally-/Unproven) from proven's own MODULE-STATUS.txt + STATE.a2ml OWED ledger, without re-checking proofs. As-declared 4/37/47 reconciles with MODULE-STATUS; strict evidence-carrying grading reports 0 Actually-Proven (the 4 proof-bearing modules all carry OWED axioms). See that repo's integrations/proven and .machine_readable/6a2/ECOSYSTEM.a2ml." },
+]