Add version logging and route decision logging to sx-browser

boot-init prints SX_VERSION (build timestamp) to console on startup.
tryClientRoute logs why it falls through: has-data, no content, eval
failed, #main-panel not found. tryEvalContent logs the actual error.
Added logWarn platform function.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/ref/boot.sx

@@ -336,6 +336,7 @@
     ;; 5. Hydrate [data-sx] elements
     ;; 6. Process engine elements
     (do
+      (log-info (str "sx-browser " SX_VERSION))
       (init-css-tracking)
       (init-style-dict)
       (process-sx-scripts nil)