Detect text files via MIME + binary heuristic instead of hardcoded extension list

Server-side _file_type() now uses mimetypes for images/known text,
and falls back to null-byte check on first 8KB for everything else.
Client uses the "type" field from /files API instead of local extension sets.

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

static/index.html

@@ -259,10 +259,7 @@ $('lang-sw').addEventListener('click', e => {
   if (e.target.dataset.l) setLang(e.target.dataset.l);
 });
 
-const TEXT_EXT = new Set(
-  'txt,log,json,xml,csv,html,css,js,ts,py,md,sh,yml,yaml,toml,ini,cfg,conf,env,sql,rs,go,java,c,h,cpp,rb,php'.split(',')
-);
-const IMG_EXT = new Set('png,jpg,jpeg,gif,webp,bmp,ico,svg'.split(','));
+/* File type is determined server-side via /files API ("text" | "image" | "other") */
 
 /* ── Helpers ── */
 
@@ -287,10 +284,6 @@ function esc(s) {
           .replace(/"/g,'"').replace(/'/g,''');
 }
 
-function fileExt(name) {
-  return (name.split('.').pop() || '').toLowerCase();
-}
-
 /* ── Clipboard ── */
 
 function fallbackCopy(text) {
@@ -332,15 +325,14 @@ function toPngBlob(blob) {
   });
 }
 
-function copyFile(name) {
+function copyFile(name, type) {
   const url = '/dl/' + encodeURIComponent(name);
-  const ext = fileExt(name);
 
-  if (TEXT_EXT.has(ext)) {
+  if (type === 'text') {
     fetch(url).then(r => r.text()).then(text => copyText(text))
       .catch(() => toast(t().copyFail));
 
-  } else if (IMG_EXT.has(ext)) {
+  } else if (type === 'image') {
     const link = location.origin + url;
     if (!navigator.clipboard?.write) {
       copyText(link, t().linkCopied);
@@ -457,7 +449,7 @@ function renderFiles() {
 
   flist.innerHTML = slice.map(f => `
     <div class="file">
-      <span class="fname" data-action="copy" data-name="${esc(f.name)}" title="${t().copy}">${esc(f.name)}</span>
+      <span class="fname" data-action="copy" data-name="${esc(f.name)}" data-type="${f.type}" title="${t().copy}">${esc(f.name)}</span>
       <div class="meta">
         <span class="fsize">${fmtSize(f.size)}</span>
         <a class="btn dl" href="/dl/${encodeURIComponent(f.name)}" title="${t().download}"><svg width="14" height="14"><use href="#icon-dl"/></svg></a>
@@ -482,7 +474,7 @@ flist.addEventListener('click', e => {
   if (!el) return;
   const action = el.dataset.action;
   const name = el.dataset.name;
-  if (action === 'copy') copyFile(name);
+  if (action === 'copy') copyFile(name, el.dataset.type);
   else if (action === 'del') {
     fetch('/del/' + encodeURIComponent(name), { method: 'DELETE' })
       .then(() => { toast(t().deleted); loadFiles() });