feat: conformance test runner + protocol fixes

- conformance.py: declarative scenario runner (subset matcher, $kind/$gt/
  $enum/$required assertions, call_id/session_id echo checks), reference
  bridge, CLI entry (python -m aicc.conformance)
- bridge.py: protocol version check before parsing (protocol_mismatch),
  session expiry handling (session_expired), malformed tool_call ->
  invalid_input, emit_event() for async events
- client.py: Self return type
- in_process.py: drain bridge event queue after response (event delivery),
  Self return type
- websocket.py: Self return type, best-effort shutdown
- tests: 14 passing (incl. conformance scenarios, 9/9 core scenarios)
- ruff: all checks pass

README.md

@@ -93,12 +93,33 @@ aicc/
   bridge.py       # Bridge — environment side, tool registration
   tool.py         # @tool decorator and tool metadata
   schema.py       # JSON Schema generation utilities
+  conformance.py  # declarative scenario runner (AICC conformance tests)
   transport/
     base.py           # Transport interface
     in_process.py     # In-process transport (tests, embedded)
     websocket.py      # WebSocket transport (client + server)
 ```
 
+## Conformance
+
+`aicc-py` ships the reference conformance runner for the AICC protocol.
+It executes the declarative scenarios from the
+[AICC-Protocol](https://github.com/emil28092005/AICC-Protocol)
+`conformance/scenarios/` directory against any bridge:
+
+```bash
+python -m aicc.conformance ~/AICC-Protocol/conformance/scenarios
+```
+
+Or via pytest (scenarios are loaded automatically if the spec repo is
+checked out next to `aicc-py`):
+
+```bash
+pytest tests/test_conformance.py
+```
+
+A bridge is AICC-conformant for `aicc/0.1` when all core scenarios pass.
+
 ## Development
 
 ```bash