Fix WebConfig bootstrap for legacy Android Chrome

Physical LG Android 5.1.1 testing found Chrome 43 could decode gzip but failed on the bootstrap's arrow syntax. Use ES5 functions and Promises while preserving retries, version refresh, and optional abort handling. Keep Google Zopfli gzip compression at 1,000 iterations.

Verified the flashed V4.3 through its WiFi link using the real Android browser: bootstrap and main page gzip responses completed, settings loaded at 910.525 MHz, and no JavaScript or transfer errors were reported. Add a loader syntax regression and document legacy browser support.

scripts/generate_webconfig_html.py

@@ -135,16 +135,19 @@ def main():
     loader = ("<!doctype html><meta charset=utf-8><meta name=viewport "
               "content=\"width=device-width,initial-scale=1\"><title>MeshCore "
               "WebConfig</title><body>Loading MeshCore WebConfig&hellip;<script>"
-              "(async()=>{let p;for(let n=0;n<3&&p===undefined;n++){const C="
-              "window.AbortController,c=C&&new C(),t=c&&setTimeout(()=>c.abort()"
-              ",90000);try{const r=await fetch(\"/ui?v=%s\",c?{signal:c.signal}"
-              ":{});if(r.ok)p=await r.text();else if(r.status===409)return "
-              "location.reload()}catch(e){}finally{if(t)clearTimeout(t)}if(p==="
-              "undefined)await new Promise(r=>setTimeout(r,500*(n+1)))}if(p==="
-              "undefined)throw Error(\"transfer failed\");document.open();"
-              "document.write(p);document.close()})().catch(e=>"
+              # Android 5.1's stock Chrome 43 supports fetch and Promises, but
+              # cannot parse arrows or async functions. Match the main UI's
+              # ES5 syntax so the bootstrap cannot strand those browsers.
+              "(function(){var n=0;function load(){var C=window.AbortController,"
+              "c=C&&new C(),t=c&&setTimeout(function(){c.abort()},90000);"
+              "fetch(\"/ui?v=%s\",c?{signal:c.signal}:{}).then(function(r){"
+              "if(r.ok)return r.text();if(r.status===409){location.reload();"
+              "return null}throw Error(\"transfer failed\")}).then(function(p){"
+              "if(t)clearTimeout(t);if(p===null)return;document.open();"
+              "document.write(p);document.close()},function(e){"
+              "if(t)clearTimeout(t);if(++n<3)setTimeout(load,500*n);else "
               "document.body.textContent=\"Unable to load WebConfig: \"+e+"
-              "\". Reload to retry.\")</script>" % version)
+              "\". Reload to retry.\"})}load()})()</script>" % version)
     loader_bytes = compress_page(loader.encode("utf-8"))
     success_bytes = compress_page(b"<HTML><HEAD><TITLE>Success</TITLE></HEAD><BODY>Success</BODY></HTML>")
     etag = hashlib.sha256(loader_bytes).hexdigest()[:16]