skill-loader export fix + TUI config panel + provider test + slot descriptions

- Fix skill loader export: unintern before import (handle existing symbols)
- Add ignore-errors around export (handle package conflicts)
- Add test-provider-connection (live API key testing for TUI config)
- Add *slot-descriptions* with per-slot explanations for TUI config screen
- Rewrite gateway-tui with expanding minibuffer config panel (F2 toggle)
- Fix skill loader exclusion list: add system-model-router
- All org files updated with proper prose

org/system-model-provider.org

@@ -116,6 +116,33 @@ Providers register themselves at boot. No API key? That provider doesn't registe
                                                            *provider-configs*))))))
 #+end_src
 
+** Provider connection test (for TUI config)
+;; REPL-verified: 2026-05-04
+#+begin_src lisp
+(defun test-provider-connection (provider &optional api-key)
+  "Test a provider API key by hitting its models endpoint.
+Returns (:ok) on success, (:fail reason) on failure.
+If API-KEY is nil, reads from environment."
+  (let* ((config (provider-config provider))
+         (base-url (getf config :base-url))
+         (key-env (getf config :key-env))
+         (url-env (getf config :url-env))
+         (key (or api-key (when key-env (uiop:getenv key-env)))))
+    (handler-case
+        (let ((url (if url-env
+                       (let ((host (or (uiop:getenv url-env) "")))
+                         (format nil "http://~a/api/tags" host))
+                       (format nil "~a/models" (or base-url "")))))
+          (if key-env
+              (progn (dex:get url :headers `(("Authorization" . ,(format nil "Bearer ~a" key)))
+                              :connect-timeout 5 :read-timeout 10)
+                     '(:ok))
+              (if url-env
+                  (progn (dex:get url :connect-timeout 5 :read-timeout 10) '(:ok))
+                  '(:fail "No URL source for this provider"))))
+      (error (c) `(:fail ,(format nil "~a" c))))))
+#+end_src
+
 ** Boot registration
 #+begin_src lisp
 (provider-register-all)