feat(downloads): live per-file progress on running events — #709

Now that we own the walk, surface live counts on the in-flight download in the
Downloads view. ingest_core.run takes an event_id and does a TIME-THROTTLED
write (~5s, decoupled from page boundaries so it ticks steadily regardless of
how big/slow a page is) of {downloaded, skipped, errors, quarantined, posts} to
the running download_event's metadata.live (jsonb_set; short session; status
guard so a finalized event isn't clobbered). download_backends threads
event_id from ctx; the /api/downloads list surfaces `live`; ActiveDownloadsPanel
renders it beside the elapsed timer. Native (Patreon) only — gallery-dl is an
opaque subprocess; the row only shows when `live` is present. Phase 3 overwrites
metadata with run_stats on finish, dropping `live`.

Test: _write_live_progress updates a running event's metadata.live and leaves a
finalized (status != running) event alone.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/components/subscriptions/ActiveDownloadsPanel.vue

@@ -23,6 +23,18 @@
         <span class="fc-active__dot" />
         <PlatformChip :platform="e.platform" size="x-small" />
         <span class="fc-active__artist">{{ e.artist_name || '—' }}</span>
+        <!-- #709: live per-file progress for native (Patreon) downloads. -->
+        <span v-if="e.live" class="fc-active__counts">
+          <span class="fc-active__count" title="downloaded">↓ {{ e.live.downloaded }}</span>
+          <span v-if="e.live.skipped" class="fc-active__count" title="skipped">
+            ⤼ {{ e.live.skipped }}</span>
+          <span
+            v-if="e.live.errors" class="fc-active__count fc-active__count--err"
+            title="errors"
+          >✕ {{ e.live.errors }}</span>
+          <span class="fc-active__count fc-active__count--posts" title="posts scanned">
+            {{ e.live.posts }} posts</span>
+        </span>
         <v-spacer />
         <span class="fc-active__timer" :title="`started ${e.started_at}`">
           {{ elapsed(e.started_at) }}
@@ -123,6 +135,13 @@ function elapsed (startedIso) {
   font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.05em;
   color: rgb(var(--v-theme-on-surface-variant));
 }
+.fc-active__counts {
+  display: inline-flex; align-items: center; gap: 8px;
+  font-variant-numeric: tabular-nums; font-size: 0.78rem;
+}
+.fc-active__count { color: rgb(var(--v-theme-on-surface-variant)); }
+.fc-active__count--err { color: rgb(var(--v-theme-error)); }
+.fc-active__count--posts { opacity: 0.7; }
 @keyframes fc-active-pulse {
   0%, 100% { opacity: 1; transform: scale(1); }
   50% { opacity: 0.35; transform: scale(0.7); }