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/bootstrap_js.py

@@ -476,6 +476,7 @@ class JSEmitter:
             "process-sx-scripts": "processSxScripts",
             "process-component-script": "processComponentScript",
             "init-style-dict": "initStyleDict",
+            "SX_VERSION": "SX_VERSION",
             "boot-init": "bootInit",
             "resolve-mount-target": "resolveMountTarget",
             "sx-render-with-env": "sxRenderWithEnv",
@@ -1288,7 +1289,9 @@ def compile_ref_to_js(
         parts.append(CONTINUATIONS_JS)
     parts.append(public_api_js(has_html, has_sx, has_dom, has_engine, has_orch, has_cssx, has_boot, has_parser, adapter_label, has_deps, has_router))
     parts.append(EPILOGUE)
-    return "\n".join(parts)
+    from datetime import datetime, timezone
+    build_ts = datetime.now(timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ")
+    return "\n".join(parts).replace("BUILD_TIMESTAMP", build_ts)
 
 
 # ---------------------------------------------------------------------------
@@ -1312,6 +1315,7 @@ PREAMBLE = '''\
   // =========================================================================
 
   var NIL = Object.freeze({ _nil: true, toString: function() { return "nil"; } });
+  var SX_VERSION = "BUILD_TIMESTAMP";
 
   function isNil(x) { return x === NIL || x === null || x === undefined; }
   function isSxTruthy(x) { return x !== false && !isNil(x); }