docs(P36): schemas/adapters/pipelines READMEs (REQ-97, REQ-98, REQ-99)

---ci---
project: acdl
phase: 36
milestone: v1.8
status: execute
---/ci---

- schemas/README.md: how to write schemas, wire into platform, test in
  CI, dependencies, existing catalog, adding a new schema.
- pipelines/README.md: how to write pipeline contracts, wire into
  workflows, test, dependencies, existing catalog, adding a new pipeline.
- adapters/README.md: how to write adapters (Terraform + policy patterns),
  wire into platform, test, dependencies, existing catalog, adding a new
  adapter.
- tests/test_docs_coverage.py: 6 tests validating all 3 READMEs exist
  with required sections.

Tests: +6 (344 -> 350). All pass.

tests/test_docs_coverage.py

@@ -0,0 +1,37 @@
+"""Validate that path documentation READMEs exist and have required sections (REQ-97, 98, 99)."""
+
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parent.parent
+
+
+class TestDocsCoverage:
+    def test_schemas_readme_exists(self):
+        assert (ROOT / "schemas" / "README.md").is_file()
+
+    def test_schemas_readme_has_required_sections(self):
+        content = open(ROOT / "schemas" / "README.md").read()
+        assert "How to Write a Schema" in content
+        assert "How to Wire" in content
+        assert "How to Test" in content
+        assert "Existing Schemas" in content
+
+    def test_pipelines_readme_exists(self):
+        assert (ROOT / "pipelines" / "README.md").is_file()
+
+    def test_pipelines_readme_has_required_sections(self):
+        content = open(ROOT / "pipelines" / "README.md").read()
+        assert "How to Write a Pipeline" in content
+        assert "How to Wire" in content
+        assert "How to Test" in content
+        assert "Existing Pipelines" in content
+
+    def test_adapters_readme_exists(self):
+        assert (ROOT / "adapters" / "README.md").is_file()
+
+    def test_adapters_readme_has_required_sections(self):
+        content = open(ROOT / "adapters" / "README.md").read()
+        assert "How to Write an Adapter" in content
+        assert "How to Wire" in content
+        assert "How to Test" in content
+        assert "Existing Adapters" in content