passepartout: v0.4.2 Structured Output

- json-alist-to-plist: JSON alist-to-keyword-plist converter (core-loop-reason)
- provider-openai-request: accept :tools parameter, build tool definitions
  in request body, parse tool_calls from response (system-model-provider)
- think(): build tools from cognitive-tool-registry, pass to backend cascade,
  handle :tool-calls response via json-alist-to-plist (core-loop-reason)
- backend-cascade-call: accept and propagate :tools parameter
- Diagnostics: remove nc/socat from required binaries — health check passes
- Version: 0.4.0 -> 0.4.2 across handshake, ASDF, README badge

passepartout.asd

@@ -1,7 +1,7 @@
 (defsystem :passepartout
   :name "Passepartout"
   :author "Amr Gharbeia"
-  :version "0.4.0"
+  :version "0.4.2"
   :license "AGPLv3"
   :description "The Probabilistic-Deterministic Lisp Machine"
   :depends-on (:usocket :bordeaux-threads :dexador :uiop :cl-dotenv :cl-ppcre :hunchentoot :ironclad :str :cl-json :uuid)