Language detection: switch to go-enry with hint-seeded classifier (#41)

- Add github.com/go-enry/go-enry/v2 dependency to go.mod
- guessLang: JSON fast path, then enry strategies (shebangs, XML, modelines,
  content heuristics), then enry's Linguist-trained Bayesian classifier over
  regex-hint candidate languages; curated dropdown expanded with typescript,
  html, css, xml, php, ruby, perl, lua, dockerfile, toml, ini, diff, csharp
- enry display names normalized to lowercase stored ids (Dockerfile->dockerfile,
  Shell->bash, C#->csharp); unsupported languages render unhighlighted
- Tests: existing languages, all new languages, magic markers (enry shebang/
  DOCTYPE/FROM/diff handling), canonical mapping

web/templates/new.html

@@ -7,9 +7,12 @@
         <input id="title" placeholder="Title">
         <select id="language">
           <option value="">auto</option>
-          <option>go</option><option>python</option><option>javascript</option>
-          <option>rust</option><option>c</option><option>cpp</option><option>java</option>
+          <option>go</option><option>python</option><option>javascript</option><option>typescript</option>
+          <option>rust</option><option>c</option><option>cpp</option><option>java</option><option>csharp</option>
           <option>bash</option><option>sql</option><option>yaml</option><option>json</option>
+          <option>html</option><option>css</option><option>xml</option><option>php</option>
+          <option>ruby</option><option>perl</option><option>lua</option><option>dockerfile</option>
+          <option>toml</option><option>ini</option><option>diff</option>
           <option>markdown</option><option>text</option>
         </select>
         <button class="btn btn-icon" id="reguess" title="Re-detect language" type="button"><svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2.4" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M21 12a9 9 0 1 1-2.64-6.36"/><polyline points="21 3 21 9 15 9"/></svg></button>
@@ -97,9 +100,12 @@ function showResult(html, isError) {
 }
 function defaultFilename(lang) {
   const names = {
-    python: 'Python.py', go: 'main.go', javascript: 'script.js', rust: 'main.rs',
-    c: 'main.c', cpp: 'main.cpp', java: 'Main.java', bash: 'script.sh',
-    sql: 'query.sql', yaml: 'config.yaml', json: 'data.json',
+    python: 'Python.py', go: 'main.go', javascript: 'script.js', typescript: 'index.ts',
+    rust: 'main.rs', c: 'main.c', cpp: 'main.cpp', java: 'Main.java', bash: 'script.sh',
+    sql: 'query.sql', yaml: 'config.yaml', json: 'data.json', html: 'index.html',
+    css: 'style.css', xml: 'doc.xml', php: 'index.php', ruby: 'main.rb',
+    perl: 'main.pl', lua: 'main.lua', dockerfile: 'Dockerfile', toml: 'config.toml',
+    ini: 'config.ini', diff: 'changes.diff',
     markdown: 'notes.md', text: 'Text.txt',
   };
   return names[lang] || '';