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and the first thing to go out of date.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/RuleListPane.vue

@@ -17,7 +17,17 @@ const emit = defineEmits<{
           {{ r.title }}
           <!-- Only conditional is marked: always-on is the default and
                badging every row would say nothing. -->
-          <span v-if="r.tier === 'conditional'" class="tier-chip" title="Arrives when its trigger fires, rather than in every session">conditional</span>
+          <span v-if="r.tier === 'conditional'" class="rule-chip" title="Arrives when its trigger fires, rather than in every session">conditional</span>
+          <!-- Present only on a rule carrying a check, so the chip's very
+               presence says "this one asserts a fact that can go false". -->
+          <span
+            v-if="r.last_verified"
+            class="rule-chip check-chip"
+            :class="{ unchecked: r.last_verified === 'never' }"
+            :title="r.last_verified === 'never'
+              ? 'Asserts a fact nobody has confirmed yet'
+              : `Check last passed ${r.last_verified}`"
+          >{{ r.last_verified === "never" ? "unverified" : `checked ${r.last_verified}` }}</span>
         </div>
         <div class="statement">{{ r.statement }}</div>
         <div v-if="r.when_to_apply || r.updated_at" class="meta">
@@ -47,16 +57,13 @@ li:hover { background: var(--fs-surface-hover); }
 .meta { display: flex; align-items: baseline; gap: 0.5rem; margin-top: 0.35rem; font-size: 0.75em; }
 .trigger { flex: 1; min-width: 0; color: var(--fs-text-secondary); overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
 .age { color: var(--fs-text-tertiary); font-variant-numeric: tabular-nums; flex-shrink: 0; }
-.tier-chip {
-  margin-left: 0.4rem;
-  font-family: var(--fs-font-body);
-  font-style: normal;
-  font-size: 0.62rem;
-  color: var(--fs-text-secondary);
-  background: var(--fs-surface-raised);
-  border-radius: var(--fs-radius-pill);
-  padding: 0.05rem 0.4rem;
-  vertical-align: middle;
-}
+/* Only the departures from .rule-chip (rules-shared.css) live here. */
+.check-chip { font-variant-numeric: tabular-nums; }
+/* No age-graded colour on purpose. 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. Only "never" is marked, because it is categorically
+   different from a date rather than a worse one. */
+.check-chip.unchecked { font-style: italic; color: var(--fs-text-tertiary); }
 .new-rule { cursor: pointer; }
 </style>