Dashboard: content + source-health; per-viewer local dates

* Date fix: introduce GOODNEWS_TZ (goodnews/localtime.py) so the brief's "today"
  rolls over in a pinned zone (Eastern) instead of UTC — robust to host-clock
  resets. The home page now formats the brief's date in each VISITOR's local
  timezone (from its UTC freshness stamp), so nobody ever sees "tomorrow."

* Admin "Content served": articles live, fresh (7d), ingested (24h), summaries,
  active sources, today's brief size — queries.content_stats().

* Admin "Source health": per active source, the failure streak, last error,
  accepted contribution, and computed next-poll time (so backoff / "resting
  until" is visible), via queries.source_health() reusing the feeds backoff
  math. Failing sources sort to the top; times render in the viewer's zone.

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

frontend/src/routes/+page.svelte

@@ -76,6 +76,17 @@
 
   const cap = (s) => (s ? s[0].toUpperCase() + s.slice(1) : s);
   const humanize = (s) => (s || '').replace(/-/g, ' ');
+
+  // Show the brief's date in the VIEWER's local timezone (from its UTC freshness
+  // stamp), so everyone sees their own correct date — never "tomorrow."
+  function localDateLabel(b) {
+    const ts = b?.generated_at;
+    if (ts) {
+      const d = new Date(ts.replace(' ', 'T') + 'Z');
+      if (!isNaN(d)) return d.toLocaleDateString(undefined, { weekday: 'long', month: 'long', day: 'numeric' });
+    }
+    return b?.brief_date ?? '';
+  }
   let filtersOn = $derived(prefsActive());
   let currentMood = $derived(moods.find((m) => m.key === selected));
   let currentTopic = $derived(topics.find((t) => t.key === selected));
@@ -89,7 +100,7 @@
         : (currentMood?.label ?? cap(currentTopic?.key) ?? '')
   );
   let viewSubtitle = $derived(
-    selected === 'today' ? (brief?.brief_date ?? '')
+    selected === 'today' ? localDateLabel(brief)
       : currentTag ? (tagFamily?.description ?? '')
         : (currentMood?.description ?? currentTopic?.description ?? '')
   );