fix(dashboard): copy buttons fall back to execCommand when clipboard API blocked

Three pages had `navigator.clipboard.writeText(...)` with no fallback and
no .catch() — when the modern API is unavailable (HTTP non-localhost,
permissions denied, focus loss, browser blocking) the click was a silent
no-op. User reported the chat-prompt copy button doing nothing.

Fixed in:
  codec_chat.html       copyMsgText()  (chat message copy buttons)
  codec_dashboard.html  copyText()     (overview / recents card copy buttons)
  codec_vibe.html       doCopy()       (code editor copy)

Each now:
  1. Tries navigator.clipboard.writeText() if present
  2. On rejection / unavailability, falls back to a hidden textarea +
     document.execCommand('copy')
  3. Always surfaces a toast — "Copied" on success, "Copy failed" on
     total failure (instead of silent no-op)

Dashboard serves the HTML fresh per-request with _NO_CACHE headers, so
no PM2 restart is required — a browser refresh picks up the fix.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Mikarina13

codec_chat.html

@@ -488,7 +488,28 @@ <h1><a href="/" style="color:inherit;text-decoration:none">CODEC</a></h1>
 var thinkingEnabled=true;
 
 function showToast(msg){var t=document.getElementById('toast');t.textContent=msg;t.classList.add('show');setTimeout(function(){t.classList.remove('show')},1800)}
-function copyMsgText(text,btn){navigator.clipboard.writeText(text).then(function(){btn.classList.add('copied');showToast('Copied');setTimeout(function(){btn.classList.remove('copied')},1500)})}
+function _copyFallback(text){
+  try{
+    var ta=document.createElement('textarea');
+    ta.value=text;
+    ta.setAttribute('readonly','');
+    ta.style.position='fixed';
+    ta.style.top='0';ta.style.left='0';
+    ta.style.opacity='0';ta.style.pointerEvents='none';
+    document.body.appendChild(ta);
+    ta.focus();ta.select();ta.setSelectionRange(0,ta.value.length);
+    var ok=document.execCommand('copy');
+    document.body.removeChild(ta);
+    return ok;
+  }catch(e){return false}
+}
+function copyMsgText(text,btn){
+  function ok(){btn.classList.add('copied');showToast('Copied');setTimeout(function(){btn.classList.remove('copied')},1500)}
+  function fail(){if(_copyFallback(text)){ok()}else{showToast('Copy failed')}}
+  if(navigator.clipboard&&navigator.clipboard.writeText){
+    navigator.clipboard.writeText(text).then(ok,fail).catch(fail)
+  }else{fail()}
+}
 
 function setMode(mode){
   var changed=chatMode!==mode;

codec_dashboard.html

@@ -776,12 +776,48 @@ <h2>MENU</h2>
 }
 
 // ── Copy to clipboard ──
+// Two-path implementation: prefer navigator.clipboard (secure-context API),
+// fall back to a hidden textarea + document.execCommand('copy') if the
+// modern API is unavailable (HTTP non-localhost) or the promise rejects
+// (permissions, focus loss, etc.). Always surfaces a toast — success or
+// failure — so the click is never silent.
+function _copyFallback(text) {
+  try {
+    var ta = document.createElement('textarea');
+    ta.value = text;
+    ta.setAttribute('readonly', '');
+    ta.style.position = 'fixed';
+    ta.style.top = '0';
+    ta.style.left = '0';
+    ta.style.opacity = '0';
+    ta.style.pointerEvents = 'none';
+    document.body.appendChild(ta);
+    ta.focus();
+    ta.select();
+    ta.setSelectionRange(0, ta.value.length);
+    var ok = document.execCommand('copy');
+    document.body.removeChild(ta);
+    return ok;
+  } catch (e) {
+    return false;
+  }
+}
+
 function copyText(text, btn) {
-  navigator.clipboard.writeText(text).then(function() {
+  function onOk() {
     btn.classList.add('copied');
     showToast('Copied to clipboard');
     setTimeout(function() { btn.classList.remove('copied'); }, 1500);
-  });
+  }
+  function onFail() {
+    if (_copyFallback(text)) { onOk(); }
+    else { showToast('Copy failed — clipboard not available'); }
+  }
+  if (navigator.clipboard && navigator.clipboard.writeText) {
+    navigator.clipboard.writeText(text).then(onOk, onFail).catch(onFail);
+  } else {
+    onFail();
+  }
 }
 
 // ── Theme ──

codec_vibe.html

@@ -957,10 +957,32 @@ <h1><a href="/" style="color:inherit;text-decoration:none">CODEC</a></h1>
   });
 }
 
+function _copyFallback(text){
+  try{
+    var ta=document.createElement('textarea');
+    ta.value=text;ta.setAttribute('readonly','');
+    ta.style.position='fixed';ta.style.top='0';ta.style.left='0';
+    ta.style.opacity='0';ta.style.pointerEvents='none';
+    document.body.appendChild(ta);ta.focus();ta.select();
+    ta.setSelectionRange(0,ta.value.length);
+    var ok=document.execCommand('copy');
+    document.body.removeChild(ta);return ok;
+  }catch(e){return false}
+}
 function doCopy() {
-  navigator.clipboard.writeText(ed.getValue());
-  document.getElementById('rs').textContent = 'Copied!';
-  setTimeout(function() { document.getElementById('rs').textContent = ''; }, 2000);
+  var text = ed.getValue();
+  function ok(){
+    document.getElementById('rs').textContent = 'Copied!';
+    setTimeout(function() { document.getElementById('rs').textContent = ''; }, 2000);
+  }
+  function fail(){
+    if(_copyFallback(text)){ok()}
+    else{document.getElementById('rs').textContent='Copy failed';
+         setTimeout(function(){document.getElementById('rs').textContent='';},2000);}
+  }
+  if (navigator.clipboard && navigator.clipboard.writeText) {
+    navigator.clipboard.writeText(text).then(ok, fail).catch(fail);
+  } else { fail(); }
 }
 
 // Sidebar