fix(sdk): correct WebSocket URL pattern for platform-agent

AgentApiWrapper._build_ws_url was building /v1/agent_ws/{chat_id}/
which does not exist in platform-agent. Fixed to /agent_ws/?thread_id={chat_id}
to match the actual endpoint and query-param isolation scheme.

Also simplify Matrix MVP settings handlers to MVP_UNAVAILABLE stubs
and add handle_unknown_command for unregistered !commands.

.dockerignore

@@ -0,0 +1,17 @@
+.git
+.gitignore
+.DS_Store
+__pycache__/
+.pytest_cache/
+.ruff_cache/
+.venv/
+.worktrees/
+
+# Local runtime state must not be baked into the image.
+lambda_matrix.db
+matrix_store/
+lambda_bot.db
+
+# Local environment and editor state
+.env
+.idea/