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

lisp/core-communication.lisp

@@ -62,7 +62,7 @@
   (let ((stream (usocket:socket-stream socket)))
     (handler-case
         (progn
-          (format stream "~a" (frame-message (make-hello-message "0.4.0")))
+          (format stream "~a" (frame-message (make-hello-message "0.4.2")))
           (finish-output stream)
           (loop
             (let ((msg (read-framed-message stream)))