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

org/system-diagnostics.org

@@ -34,7 +34,7 @@ Binary detection must use shell probing (`which`) to account for varying `$PATH`
 ** Global Configuration
 ;; REPL-VERIFIED: 2026-05-03T13:00:00
 #+begin_src lisp
-(defvar *diagnostics-binaries* '("sbcl" "emacs" "git" "socat" "nc")
+(defvar *diagnostics-binaries* '("sbcl" "emacs" "git")
   "List of external binaries required for full system operation.")
 
 #+end_src
@@ -45,8 +45,6 @@ Binary detection must use shell probing (`which`) to account for varying `$PATH`
   '(("sbcl" . "sbcl")
     ("emacs" . "emacs")
     ("git" . "git")
-    ("socat" . "socat")
-    ("nc" . "netcat-openbsd")
     ("curl" . "curl")
     ("rlwrap" . "rlwrap"))
   "Map binary names to apt package names.")