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/static/app.css

@@ -95,10 +95,13 @@ body {
   border: 1px solid var(--border); background: var(--surface-2); color: var(--muted-fg);
   border-radius: var(--radius); padding: 4px 10px; font: inherit; font-size: 21.6px; cursor: pointer;
 }
+/* shared code line metrics (#50): gutter + code must share one line box */
+:root { --code-lh: 1.7; --code-fs: 21.6px; }
+
 .editor-wrap { flex: 1; display: flex; min-height: 0; }
 .gutter {
   padding: 14px 10px; text-align: right; color: var(--muted); font-family: var(--font-mono);
-  font-size: 21.6px; line-height: 1.7; user-select: none; white-space: pre; overflow: hidden;
+  font-size: var(--code-fs); line-height: var(--code-lh); user-select: none; white-space: pre; overflow: hidden;
   border-right: 1px solid var(--border);
 }
 .editor {
@@ -145,11 +148,12 @@ body {
 .paste-title-bar { display: flex; align-items: center; gap: 12px; padding: 12px 18px; flex-wrap: wrap; }
 .paste-title-bar h1 { font-size: 29.2px; font-weight: 600; margin: 0; }
 .stats-pill { border: 1px solid var(--border); border-radius: var(--radius); overflow: hidden; }
-.stats-head { display: flex; align-items: center; gap: 10px; width: 100%; background: none; border: 0; color: var(--muted-fg); font: inherit; font-size: 21.6px; padding: 10px 14px; cursor: pointer; text-align: left; }
+.stats-head { display: flex; align-items: center; gap: 16px; width: 100%; background: none; border: 0; color: var(--muted-fg); font: inherit; font-size: 21.6px; padding: 14px 18px; cursor: pointer; text-align: left; }
 .stats-head:hover { color: var(--fg); background: var(--surface-2); }
 .stats-chev { width: 18px; height: 18px; flex: none; transition: transform 0.15s ease; }
 .stats-pill.open .stats-chev { transform: rotate(180deg); }
-.stats-summary { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
+.stats-summary { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; letter-spacing: .01em; }
+@media (max-width: 640px) { .stats-summary { white-space: normal; word-break: break-word; } }
 .stats-body { border-top: 1px solid var(--border); }
 .stats-grid { display: grid; grid-template-columns: max-content 1fr; gap: 6px 18px; padding: 12px 16px; font-size: 20.7px; }
 .stats-k { color: var(--muted-fg); }
@@ -169,10 +173,12 @@ body {
 }
 .code-head .dot { width: 8px; height: 8px; border-radius: 50%; background: var(--accent); }
 .code {
-  font-family: var(--font-mono); font-size: 22.4px; line-height: 1.7;
+  font-family: var(--font-mono); font-size: var(--code-fs); line-height: var(--code-lh);
   padding: 14px 0; display: flex; overflow-x: auto;
 }
 .code .gutter { flex-shrink: 0; }
+/* gutter/code share line metrics; the editor gutter keeps its own padding (#50) */
+.code .gutter { padding-top: 0; padding-bottom: 0; }
 .codebody { padding: 0 18px; white-space: pre; }
 /* syntax highlight tokens (#1) */
 .tok-kw { color: #c792ea; }
@@ -370,6 +376,12 @@ th.sorted.desc .sort-ind { border-top: 6px solid var(--accent); }
   outline-offset: 1px;
 }
 
+/* in-place copy success feedback (#53) */
+.iconbtn.ok, .btn.ok {
+  color: var(--ok);
+  border-color: var(--ok);
+}
+
 /* headings: unified treatment (mirrors .side-section h3) */
 .settings-head h1, .paste-title-bar h1, .head-row h1, .inner h1 {
   letter-spacing: -0.01em;