Phase 4: first-run onboarding + TUI config panel improvements

- Add providers-configured-p function (daemon-side detection)
- Add welcome log messages when no LLM providers configured
- Rewrite config panel with 4 interactive sections (Providers, Cascade, Models, View)
- Add first-run welcome messages in TUI chat on connect
- Fix config-render-models paren balance

lisp/core-loop.lisp

@@ -117,6 +117,12 @@
   (actuator-initialize)
   (skill-initialize-all)
   
+  ;; Check for configured LLM providers
+  (when (zerop (hash-table-count *probabilistic-backends*))
+    (log-message "WELCOME: No LLM providers configured. Run 'passepartout tui' and press F2 to set up.")
+    (log-message "WELCOME: Supported providers: openrouter, openai, anthropic, groq, gemini, deepseek, nvidia")
+    (log-message "WELCOME: For free tier, start with OPENROUTER_API_KEY at https://openrouter.ai"))
+  
   ;; Run proactive doctor before starting services
   (diagnostics-startup-run)
   
@@ -139,6 +145,11 @@
         (return))
       (sleep sleep-interval))))
 
+(defun providers-configured-p ()
+  "Returns T if at least one probabilistic backend is registered."
+  (and (boundp '*probabilistic-backends*)
+       (> (hash-table-count *probabilistic-backends*) 0)))
+
 (eval-when (:compile-toplevel :load-toplevel :execute)
   (ql:quickload :fiveam :silent t))