feat: the announcement link, on the card and in a review queue (388 E5)

Rule 27 — E5's other half. The matcher can propose; this is where the operator
decides, and where an accepted link actually shows up.

**The review queue** (Settings → Ingestion & filters). Each proposal shows the
per-signal breakdown, not just the total: "why did it suggest this" is the
question the operator actually has, and a lone percentage cannot answer it. So
a row reads "72% · timing 95% · says so 60%", and the copy states outright that
a pair always needs two reasons — which is the property that stops a busy
posting day from producing false pairs.

The empty state says so explicitly. Nothing proposed is the EXPECTED state most
of the time, and an empty queue that looks like a failure invites turning the
threshold down until it produces noise.

**On the card**, both directions, and accepted links only: the teaser gets "The
full set is in Discord", the drop gets "Announced on Patreon". A pending
proposal is a question for the review queue, never a claim to render beside the
artwork — that distinction is the whole confirm-only design, so it is asserted
in the backend (only `linked` rows reach the payload) and again here.

One detail worth the comment it carries: the link's target is `{ query: {
post_id } }` with no name or path. In vue-router that means "the current route
with these query params", so it works identically from Latest and from Browse —
and, more usefully, the card never reaches for `useRoute()`, which it has no
other reason to know about and which is not available when it is mounted in a
test without a router.

Backend CI on 235393c was green: all 13 E5 tests and migration 0094.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LNXXULQDjVZmbuNa2G9mD9

frontend/src/components/settings/MaintenancePanel.vue

@@ -15,6 +15,7 @@
         <ImportFiltersForm />
         <TranslationCard />
         <DiscordGroupingCard />
+        <PostAssociationsCard />
       </div>
     </section>
 
@@ -82,6 +83,7 @@ import VideoEmbeddingCard from './VideoEmbeddingCard.vue'
 import CropProposersCard from './CropProposersCard.vue'
 import HeadsCard from './HeadsCard.vue'
 import DiscordGroupingCard from './DiscordGroupingCard.vue'
+import PostAssociationsCard from './PostAssociationsCard.vue'
 import GpuAgentCard from './GpuAgentCard.vue'
 import AliasTable from './AliasTable.vue'
 import BackupCard from './BackupCard.vue'