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/components/rules/RuleHistoryPanel.vue

@@ -144,10 +144,10 @@ watch(() => props.ruleId, () => { selected.value = null; load(); });
     </button>
 
     <div v-if="expanded" class="body">
-      <p v-if="loading" class="state">Loading…</p>
+      <p v-if="loading" class="sweep-state">Loading…</p>
 
       <!-- Never reworded is the ordinary case, and must not read as a fault. -->
-      <p v-else-if="!versions.length" class="state empty">
+      <p v-else-if="!versions.length" class="sweep-state empty">
         This rule has never been reworded. Nothing was recorded before the history
         existed, so an older rule starts empty too.
       </p>
@@ -172,7 +172,7 @@ watch(() => props.ruleId, () => { selected.value = null; load(); });
             </button>
 
             <div v-if="selected?.id === v.id" class="detail">
-              <p v-if="loadingDetail" class="state">Loading…</p>
+              <p v-if="loadingDetail" class="sweep-state">Loading…</p>
               <template v-else>
                 <p v-if="checkChanged(i)" class="warn">
                   This edit changed the rule's check, which cleared its verification
@@ -188,7 +188,7 @@ watch(() => props.ruleId, () => { selected.value = null; load(); });
                 </dl>
                 <h4>Statement</h4>
                 <DiffView v-if="diff.length" :diff="diff" />
-                <p v-else class="state">The statement did not change in this edit.</p>
+                <p v-else class="sweep-state">The statement did not change in this edit.</p>
               </template>
             </div>
           </li>
@@ -213,8 +213,6 @@ watch(() => props.ruleId, () => { selected.value = null; load(); });
 }
 
 .body { margin-top: var(--fs-space-3); display: flex; flex-direction: column; gap: var(--fs-space-3); }
-.state { margin: 0; font-size: var(--fs-size-body-sm); color: var(--fs-text-secondary); }
-.state.empty { color: var(--fs-text-tertiary); }
 .lede {
   margin: 0; max-width: 62ch; font-size: var(--fs-size-tiny);
   color: var(--fs-text-tertiary); line-height: var(--fs-leading-body);
@@ -271,3 +269,4 @@ watch(() => props.ruleId, () => { selected.value = null; load(); });
 }
 h4 { margin: var(--fs-space-2) 0 0; font-size: var(--fs-size-tiny); color: var(--fs-text-tertiary); }
 </style>
+<style src="@/assets/sweep-shared.css" />