docs: freeze WAVE0 domain foundation and contract governance

Mark WAVE0 FROZEN CANDIDATE for Human Review; docs + .ai domain/product only — no apps or migrations.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/WAVE0/contracts/contract_diff.template.yaml

@@ -0,0 +1,34 @@
+# contract_diff — template (P0 · required per implement ECR)
+
+# Copy to: docs/CONTRACT_DIFF/ECR-xxx.yaml
+# Guardian / Reviewer: reject coding Approve if missing or breaking without migration notes.
+
+ecr: ECR-XXX
+capability: ""          # L0 id
+bounded_context: ""     # L1 id
+change:
+  type: additive        # additive | breaking | deprecate
+breaking_change: false
+migration_required: false
+compatibility_notes: ""
+
+entities:
+  - name: ExampleEntity
+    before: null
+    after:
+      fields:
+        - id
+        - name
+
+apis:
+  - method: GET
+    path: /api/v1/admin/example
+    change: added       # added | modified | removed
+    request_delta: null
+    response_delta: null
+
+security_impact:
+  - "AdminAuth required"
+
+observability_impact:
+  - "writes AuditLog on mutate"