Implement Phase 9: client libraries (Go, Rust, Lisp, Python)

- clients/README.md: canonical API surface and error type reference
- clients/testdata/: shared JSON response fixtures
- clients/go/: mciasgoclient package; net/http + TLS 1.2+; sync.RWMutex
  token state; DisallowUnknownFields on all decoders; 25 tests pass
- clients/rust/: async mcias-client crate; reqwest+rustls (no OpenSSL);
  thiserror MciasError enum; Arc<RwLock> token state; 22+1 tests pass;
  cargo clippy -D warnings clean
- clients/lisp/: ASDF mcias-client; dexador HTTP, yason JSON; mcias-error
  condition hierarchy; Hunchentoot mock-dispatcher; 37 fiveam checks pass
  on SBCL 2.6.1; yason boolean normalisation in validate-token
- clients/python/: mcias_client package (Python 3.11+); httpx sync;
  py.typed; dataclasses; 32 pytest tests; mypy --strict + ruff clean
- test/mock/mockserver.go: in-memory mock server for Go client tests
- ARCHITECTURE.md §19: updated per-language notes to match implementation
- PROGRESS.md: Phase 9 marked complete
- .gitignore: exclude clients/rust/target/, python .venv, .pytest_cache,
  .fasl files
Security: token never logged or exposed in error messages in any library;
TLS enforced in all four languages; token stored under lock/mutex/RwLock

clients/python/mcias_client/__init__.py

@@ -0,0 +1,27 @@
+"""MCIAS Python client library."""
+from ._client import Client
+from ._errors import (
+    MciasAuthError,
+    MciasConflictError,
+    MciasError,
+    MciasForbiddenError,
+    MciasInputError,
+    MciasNotFoundError,
+    MciasServerError,
+)
+from ._models import Account, PGCreds, PublicKey, TokenClaims
+
+__all__ = [
+    "Client",
+    "MciasError",
+    "MciasAuthError",
+    "MciasForbiddenError",
+    "MciasNotFoundError",
+    "MciasInputError",
+    "MciasConflictError",
+    "MciasServerError",
+    "Account",
+    "PublicKey",
+    "TokenClaims",
+    "PGCreds",
+]