Small fixes: gutter alignment, paste column, sort arrows, copy feedback, stats bar, title slug (#50-#55)

- #50 gutter/code line misalignment: shared --code-lh/--code-fs tokens;
  .code .gutter drops its own vertical padding (was 14px vs 0, 14px offset)
- #51 history Paste column shows only the paste name, or slug pill when untitled
- #52 sort indicator arrow sits LEFT of the column label for all sortable columns
- #53 copy buttons give in-place success feedback ('Success!' in --ok for 2s):
  paste view copy button and new-page result copy button
- #54 collapsed stats summary bar: roomier padding (14px 18px) and item gap (16px);
  wraps gracefully on mobile
- #55 paste view title bar: slug pill only shown for custom slugs, id not repeated

Closes #50, closes #51, closes #52, closes #53, closes #54, closes #55

web/templates/mine.html

@@ -57,8 +57,8 @@ async function load() {
   }
   $('empty').style.display = 'none';
   rows.innerHTML = data.items.map(it =>
-    `<tr class="row" data-href="/${esc(it.id)}"><td><a class="slug" href="/${esc(it.id)}">${esc(it.id)}</a>` +
-    (it.title ? `<div class="paste-sub">${esc(it.title)}</div>` : `<div class="paste-sub dim">none</div>`) + `</td>` +
+    `<tr class="row" data-href="/${esc(it.id)}"><td>` +
+    (it.title ? `${esc(it.title)}` : `<a class="slug" href="/${esc(it.id)}">${esc(it.id)}</a>`) + `</td>` +
     `<td><span class="badge">${esc(it.language || 'text')}</span></td>` +
     `<td class="dim">${fmtSize(it.size)}</td><td class="dim" data-ts="${it.created_at}">${ago(it.created_at)}</td>` +
     (it.custom_slug ? `<td><a class="slug url-link" href="/${esc(it.custom_slug)}">/${esc(it.custom_slug)}</a></td>` : `<td class="dim">none</td>`) +