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/lisp/conditions.lisp

@@ -0,0 +1,37 @@
+;;;; conditions.lisp -- MCIAS error condition hierarchy
+
+(in-package #:mcias-client)
+
+(define-condition mcias-error (error)
+  ((status  :initarg :status  :reader mcias-error-status
+            :documentation "HTTP status code (integer).")
+   (message :initarg :message :reader mcias-error-message
+            :documentation "Server error message string."))
+  (:report (lambda (c s)
+             (format s "MCIAS error ~A: ~A"
+                     (mcias-error-status c)
+                     (mcias-error-message c))))
+  (:documentation "Base condition for all MCIAS API errors."))
+
+(define-condition mcias-auth-error     (mcias-error) ()
+  (:documentation "401 Unauthorized -- token missing, invalid, or expired."))
+(define-condition mcias-forbidden-error (mcias-error) ()
+  (:documentation "403 Forbidden -- insufficient role."))
+(define-condition mcias-not-found-error (mcias-error) ()
+  (:documentation "404 Not Found -- resource does not exist."))
+(define-condition mcias-input-error    (mcias-error) ()
+  (:documentation "400 Bad Request -- malformed request."))
+(define-condition mcias-conflict-error (mcias-error) ()
+  (:documentation "409 Conflict -- e.g. duplicate username."))
+(define-condition mcias-server-error   (mcias-error) ()
+  (:documentation "5xx -- unexpected server error."))
+
+(defun signal-mcias-error (status message)
+  "Signal the appropriate MCIAS condition for STATUS (integer) and MESSAGE (string)."
+  (case status
+    (401 (error 'mcias-auth-error      :status status :message message))
+    (403 (error 'mcias-forbidden-error :status status :message message))
+    (404 (error 'mcias-not-found-error :status status :message message))
+    (400 (error 'mcias-input-error     :status status :message message))
+    (409 (error 'mcias-conflict-error  :status status :message message))
+    (t   (error 'mcias-server-error    :status status :message message))))