fix(ci): re-point validate-action references at the ecosystem repos

`hyperpolymath/k9-validate-action` and `hyperpolymath/a2ml-validate-action`
no longer exist as standalone repositories. Both were consolidated INTO
`k9-ecosystem` / `a2ml-ecosystem` as real top-level directories and the
originals deleted. The content is intact — 302 and 306 files respectively —
only these references are stale.

Any workflow reaching them fails at job setup with:

    Unable to resolve action hyperpolymath/k9-validate-action,
    repository not found

GitHub resolves an action held in a subdirectory as `owner/repo/path@ref`, so
this is a path change, not a restore:

    hyperpolymath/a2ml-validate-action@<old>
      -> hyperpolymath/a2ml-ecosystem@aa4b836b
    hyperpolymath/k9-validate-action@<old>
      -> hyperpolymath/k9-ecosystem@89f3c270

Both targets are verified to hold a real `action.yml`
('Validate A2ML Manifests' / 'Validate K9 Configurations').

This surfaced only because `dogfood-gate.yml` was itself invalid YAML in 71
repos, so the workflow had never run and never attempted to resolve these
actions. Repairing the parse error exposed the stale reference beneath it.

Verified before push: every edited file still parses and still yields a
`jobs:` mapping, and no `*-validate-action@` reference remains. 1
file(s) changed, all under .github/workflows.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/dogfood-gate.yml

@@ -39,7 +39,7 @@ jobs:
 
       - name: Validate A2ML manifests
         if: steps.detect.outputs.count > 0
-        uses: hyperpolymath/a2ml-validate-action@6bff6ec134fc977e86d25166a5c522ddea5c1e78 # main
+        uses: hyperpolymath/a2ml-ecosystem/validate-action@aa4b836bd969df2bc58128cb8e3d20bbc88d5e79 # main
         with:
           path: '.'
           strict: 'false'
@@ -88,7 +88,7 @@ jobs:
 
       - name: Validate K9 contracts
         if: steps.detect.outputs.k9_count > 0
-        uses: hyperpolymath/k9-validate-action@2d96f43c538964b097d159ed3a56ba5b5ceca227 # main
+        uses: hyperpolymath/k9-ecosystem/validate-action@89f3c2702f4f650a92aa7411502f38da06abd562 # main
         with:
           path: '.'
           strict: 'false'