refactor(frontend): derive the sweep-row visual language into sweep-shared.css (#3207)

The note sweep, rule sweep, preference drift and rule history panes each
restated the same row recipe in a scoped block. It now lives once in
assets/sweep-shared.css under `sweep-` names (unprefixed globals would
leak into the unrelated scoped .row-title/.lede/.age/.actions elsewhere),
imported unscoped beside each pane's own scoped remainder.

Moved only what was shared: RuleHistoryPanel takes .sweep-state and keeps
its button row head; PreferenceDrift keeps its tiny-type footnote and
overrides the action row's layout. Lede and state now use the body-sm
token instead of 0.85rem/0.9rem (13px vs 13.6/14.4px) — one value, from
the design system.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/assets/sweep-shared.css

@@ -0,0 +1,134 @@
+/* The sweep-row visual language (#3207).
+ *
+ * A "sweep" is a pane that lists records in the order they most need a human
+ * — the note verification sweep, the rule sweep, preference drift — as one
+ * raised row per record: an italic title that opens it, an age or date pushed
+ * right, a small grid of facts, and a row of plain buttons. It was written
+ * out four times, scoped, before this sheet existed.
+ *
+ * Imported UNSCOPED (`<style src="@/assets/sweep-shared.css" />`), so every
+ * class is prefixed `sweep-`: `.row-title`, `.lede`, `.age` and `.actions`
+ * also exist, scoped, in views that have nothing to do with sweeps, and an
+ * unprefixed global would leak into all of them. What a pane does
+ * differently stays in its own scoped block — spacing remainders, a `code`
+ * style — rather than growing a modifier here per pane.
+ */
+
+.sweep-lede {
+  margin: 0;
+  max-width: 62ch;
+  font-size: var(--fs-size-body-sm);
+  color: var(--fs-text-secondary);
+  line-height: var(--fs-leading-body);
+}
+
+.sweep-filters {
+  display: flex;
+  gap: var(--fs-space-5);
+  align-items: center;
+  flex-wrap: wrap;
+}
+.sweep-filter {
+  display: flex;
+  align-items: center;
+  gap: var(--fs-space-2);
+  font-size: 0.82rem;
+  color: var(--fs-text-secondary);
+}
+.sweep-filter input[type="checkbox"] { accent-color: var(--fs-accent); }
+
+.sweep-state {
+  margin: 0;
+  font-size: var(--fs-size-body-sm);
+  color: var(--fs-text-secondary);
+}
+.sweep-state.empty { color: var(--fs-text-tertiary); }
+
+.sweep-rows {
+  list-style: none;
+  margin: 0;
+  padding: 0;
+  display: flex;
+  flex-direction: column;
+  gap: var(--fs-space-3);
+}
+.sweep-row {
+  background: var(--fs-surface-raised);
+  border-radius: var(--fs-radius-md);
+  padding: var(--fs-space-3);
+}
+.sweep-row-head {
+  display: flex;
+  align-items: baseline;
+  gap: var(--fs-space-2);
+  flex-wrap: wrap;
+}
+.sweep-row-title {
+  background: none;
+  border: none;
+  padding: 0;
+  cursor: pointer;
+  font-family: Fraunces, serif;
+  font-style: italic;
+  font-size: 1.02rem;
+  color: var(--fs-text-primary);
+  text-align: left;
+}
+.sweep-row-title:hover { text-decoration: underline; }
+
+/* The ORDER carries urgency — the top of a sweep is the thing that most needs
+   a look. No red/amber ramp: it would restate the ordering and force an
+   invented "stale after N days" threshold. "Never" is marked because it is
+   categorically DIFFERENT from a date, not a worse one. */
+.sweep-age {
+  margin-left: auto;
+  font-size: 0.78rem;
+  color: var(--fs-text-secondary);
+  font-variant-numeric: tabular-nums;
+}
+.sweep-age.unchecked { font-style: italic; color: var(--fs-text-tertiary); }
+
+.sweep-check {
+  display: grid;
+  grid-template-columns: auto 1fr;
+  gap: 0.15rem var(--fs-space-3);
+  margin: var(--fs-space-3) 0 0;
+}
+.sweep-check dt {
+  font-size: 0.7rem;
+  text-transform: uppercase;
+  letter-spacing: 0.05em;
+  color: var(--fs-text-tertiary);
+}
+.sweep-check dd {
+  margin: 0;
+  font-size: 0.82rem;
+  color: var(--fs-text-primary);
+  min-width: 0;
+}
+
+.sweep-actions {
+  display: flex;
+  gap: var(--fs-space-2);
+  margin-top: var(--fs-space-3);
+}
+.sweep-actions button {
+  cursor: pointer;
+  font: inherit;
+  font-size: 0.78rem;
+  background: var(--fs-surface-page);
+  color: var(--fs-text-primary);
+  border: 1px solid var(--fs-border-color);
+  border-radius: var(--fs-radius-md);
+  padding: 0.25rem 0.6rem;
+}
+.sweep-actions button:hover:not(:disabled) { background: var(--fs-surface-hover); }
+.sweep-actions button:disabled { opacity: var(--fs-disabled-opacity); cursor: default; }
+
+.sweep-footnote {
+  margin: 0;
+  max-width: 62ch;
+  font-size: 0.78rem;
+  color: var(--fs-text-tertiary);
+  line-height: 1.45;
+}