Fix card action buttons clipped in grid view (missing position:relative)

The real cause behind the invisible redact/delete buttons: .card lacked
position:relative, so the position:absolute action buttons (delete, redact)
and the bulk-select checkbox anchored to the viewport instead of the card
and were clipped by .card overflow:hidden. They only showed in list view,
where those elements are position:static. Add position:relative to .card so
all three position within each card. Keep the 0.35 baseline opacity on the
redact button for discoverability.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

static/style.css

@@ -234,7 +234,7 @@
   .preview-meta { padding: 10px 14px; border-top: 1px solid var(--border); font-size: 11px; color: var(--muted); display: flex; gap: 10px; flex-wrap: wrap; flex-shrink: 0; }
   .preview-open-btn { margin-left: auto; background: var(--accent); color: #fff; border: none; border-radius: 5px; padding: 4px 10px; font-size: 11px; cursor: pointer; white-space: nowrap; }
   .card.selected { outline: 2px solid var(--accent); outline-offset: 2px; }
-  .card { background: var(--surface); border: 1px solid var(--border); border-radius: 10px; overflow: hidden; cursor: pointer; transition: border-color .15s, box-shadow .15s; }
+  .card { position: relative; background: var(--surface); border: 1px solid var(--border); border-radius: 10px; overflow: hidden; cursor: pointer; transition: border-color .15s, box-shadow .15s; }
   .card:hover { border-color: var(--accent); box-shadow: 0 0 0 1px var(--accent); }
   .card.list-view { display: flex; align-items: center; gap: 12px; padding: 10px 14px; border-radius: 8px; }
   .thumb-wrap { aspect-ratio: 7/9; overflow: hidden; background: var(--bg); }