rename gateway-* → system-model-* + gateway-messaging, de-ollama, add system-model-explorer

- Rename gateway-provider → system-model-provider (generic :local provider, no hardcoded ollama)
- Rename gateway-llm → system-model (model-request dispatcher)
- Rename system-embedding-gateway → system-model-embedding
- Rename gateway-manager → gateway-messaging (public api renamed to messaging-*)
- Add system-model-explorer (model discovery via OpenRouter API, cached, per-slot recommendations)
- Fix skill loader export: replace prefix-matching with fbound/boundp-based export (20 skills now export)
- Add model-router to skill-loader exclusion list (loaded via CLI)
- De-ollama: remove hardcoded assumed-available patterns from provider pipeline
- Default cascade: cloud-only (openrouter, openai, groq, gemini, deepseek, nvidia, anthropic)
- Env example: add LOCAL_BASE_URL, fix cascade order
- All org files updated with architectural prose (literate programming)

lisp/system-model.lisp

@@ -0,0 +1,16 @@
+(in-package :passepartout)
+
+(defun model-request (&key prompt system-prompt (provider :openrouter) model)
+  "Central dispatcher for LLM requests."
+  (let ((backend (gethash provider *probabilistic-backends*)))
+    (if backend
+        (handler-case
+            (funcall backend prompt system-prompt :model model)
+          (error (c)
+            (list :status :error :message (format nil "~a Failure: ~a" provider c))))
+        (list :status :error :message (format nil "Provider ~a not registered" provider)))))
+
+(defskill :passepartout-system-model
+  :priority 100
+  :trigger (lambda (ctx) (getf ctx :user-input))
+  :deterministic (lambda (action ctx) (declare (ignore ctx)) action))