fix(compliance): declare capabilities in health endpoint (#501)

feat(compliance): declare capabilities in health endpoint

The test harness reads capabilities from /health to determine which
test suites to run. Without this field, all suites are skipped,
resulting in 0/0 tests.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: andehen

sdk_compliance_adapter/adapter.py

@@ -196,6 +196,7 @@ def health():
             "sdk_name": "posthog-python",
             "sdk_version": VERSION,
             "adapter_version": "1.0.0",
+            "capabilities": ["capture_v0", "encoding_gzip"],
         }
     )