feat(rules): the check is editable, visible, and sweepable in the UI (#3098, milestone 312 step 4)

Rule 27 — the milestone was backend-only until this. Four surfaces:

RULE EDITOR — verify_with and expires_when under a legend that asks the
actual question ("Can this rule go stale?") and says empty is the normal
answer, because most rules are decisions and a form that implies a missing
field would get them filled in out of tidiness. When the SAVED rule carries
a check, the stamp shows with Still true / No longer true beside it. The
stamp reads the stored value, not the draft: an unsaved edit to the textarea
has not been run against anything.

SWEEP PANE — its own surface, not a filter on the rule list. That list can
only ever show one topic of one rulebook, and a rule that has gone false
belongs to no one rulebook; filtering it would under-report, which is the
failure this whole surface exists to catch. Reached from the rulebook list,
below the rulebooks, because that is where you go to look at rules.

RULE ROWS — a chip only on rules carrying a check, so its presence is the
signal. PROJECT RULES TAB — the check shows beside `why` when a rule has
one, read-only: that tab is the project's view of what binds it.

NO AGE-GRADED COLOUR anywhere, deliberately. The sweep is already ordered by
urgency, so a red/amber ramp would restate the ordering AND require an
invented "stale after N days" threshold — a magic number nobody could defend
and the first thing to go out of date. --fs-overdue is error red and reserved
for a broken promise like a missed due date; a verification age is not one,
and colouring it that way makes a rule someone just wrote look broken. Only
"never" is marked, because it is categorically different from a date rather
than a worse one — and it is marked by weight, not hue.

An empty sweep says "Nothing to check", not nothing: good news must not read
as a broken page.

Two chips (tier, then verification) turned out byte-identical, so .rule-chip
moves to rules-shared.css and snippet #2906 is updated to match rather than
left describing a file that has moved on. Its header comment counted the
panes it served; that count went stale the moment a fourth arrived, so it no
longer counts.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

frontend/src/components/rules/RulebookListPane.vue

@@ -3,8 +3,8 @@ import { ref } from "vue";
 import { useRulebooksStore } from "@/stores/rulebooks";
 import type { Rulebook } from "@/api/rulebooks";
 
-defineProps<{ rulebooks: Rulebook[]; selectedId: number | null }>();
-const emit = defineEmits<{ select: [id: number] }>();
+defineProps<{ rulebooks: Rulebook[]; selectedId: number | null; sweepActive: boolean }>();
+const emit = defineEmits<{ select: [id: number]; "select-sweep": [] }>();
 
 const store = useRulebooksStore();
 const isCreating = ref(false);
@@ -34,6 +34,18 @@ async function submitNew() {
         <span v-if="rb.always_on" class="always-on-badge" title="Loaded at session start">always on</span>
       </li>
     </ul>
+    <!-- Not a rulebook, and deliberately below them: a cross-cutting view over
+         every rule the operator owns. It lives here because this is where you
+         come to look at rules, and a rule that has gone false belongs to no
+         one rulebook. -->
+    <button
+      class="sweep-entry"
+      :class="{ active: sweepActive }"
+      @click="emit('select-sweep')"
+    >
+      Due for verification
+    </button>
+
     <div class="new-rulebook">
       <button v-if="!isCreating" @click="isCreating = true">+ New rulebook</button>
       <form v-else @submit.prevent="submitNew">
@@ -63,6 +75,15 @@ li:hover { background: var(--fs-surface-hover); }
   color: var(--fs-text-on-action);
   margin-left: auto;
 }
+.sweep-entry {
+  display: block; width: 100%; text-align: left;
+  margin-top: var(--fs-space-3);
+  padding: 0.5rem; border-radius: 6px;
+  background: none; border: 1px dashed var(--fs-border-color);
+  color: var(--fs-text-secondary); font: inherit; cursor: pointer;
+}
+.sweep-entry:hover { background: var(--fs-surface-hover); }
+.sweep-entry.active { background: var(--fs-accent-soft); color: var(--fs-text-primary); }
 .new-rulebook { margin-top: 1rem; }
 .new-rulebook input {
   width: 100%; margin-bottom: 0.5rem;