refactor(root): move root artefacts to their canonical locations

Applies the estate root-shape rollout: files that are not root-level by
necessity move to where their tooling and the estate canon expect them, and
every reference to them is updated in the same change.

  * .github/hooks/validate-a2ml.sh
      (from .githooks/validate-a2ml.sh)
      ->   .github/hooks/validate-a2ml.sh
  * .github/hooks/validate-k9.sh
      (from .githooks/validate-k9.sh)
      ->   .github/hooks/validate-k9.sh
  * .github/workflows/dogfood-gate.yml
  * CONTRIBUTING.adoc
      (deleted)

Verified with `git apply --check` against current main before committing; no
behaviour change intended, the Justfile entry points keep working.

Author: hyperpolymath

.githooks/validate-a2ml.sh .github/hooks/validate-a2ml.sh.githooks/validate-a2ml.sh renamed to .github/hooks/validate-a2ml.sh

@@ -40,7 +40,7 @@ jobs:
 
       - name: Validate A2ML manifests
         if: steps.detect.outputs.count > 0
-        run: bash .githooks/validate-a2ml.sh
+        run: bash .github/hooks/validate-a2ml.sh
       - name: Write summary
         run: |
           A2ML_COUNT="${{ steps.detect.outputs.count }}"
@@ -84,7 +84,7 @@ jobs:
 
       - name: Validate K9 contracts
         if: steps.detect.outputs.k9_count > 0
-        run: bash .githooks/validate-k9.sh
+        run: bash .github/hooks/validate-k9.sh
       - name: Write summary
         run: |
           K9_COUNT="${{ steps.detect.outputs.k9_count }}"