User feedback + expanded privacy-respecting admin stats

Feedback:
- feedback table; POST /api/feedback (anonymous-ok, optional category/email,
  honeypot + per-day flood cap) stores + emails the admin; GET /api/admin/feedback.
- Shared feedback store + FeedbackModal; a speech-bubble opens it from the desktop
  header, the mobile top bar (logo moves left), the footer, and /account. Feedback
  section in /admin.

Stats (additive, same privacy model — no IP/UA/referrer/raw terms):
- Event vocab: summary_viewed (fired on /a load), full_story (card → source),
  not_today/less_like_this/hide_topic, replace_used/replace_none, paywall_replace,
  paywalled_source_open. Card title/image opens /a (no double-count); history
  records via keepalive so it survives the nav.
- Dashboard: Accounts card (counts only), reading funnel (summary→source rate),
  emotional-mix & friction, paywall, returning-visitor buckets. (Health metrics
  deferred to a future monitoring dashboard.) 131 tests pass.

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

frontend/src/routes/+page.svelte

@@ -12,7 +12,7 @@
   import { auth, refresh as refreshAuth } from '$lib/auth.svelte.js';
   import { prefs, initPrefs, active as prefsActive, applyPrefAction, syncPrefsOnLogin } from '$lib/prefs.svelte.js';
   import { initHistory, deviceIds, record, loadServerHistory } from '$lib/history.svelte.js';
-  import { trackVisit } from '$lib/analytics.js';
+  import { trackVisit, track } from '$lib/analytics.js';
 
   let moods = $state([]);
   let topics = $state([]);
@@ -156,8 +156,10 @@
     if (typeof window !== 'undefined') window.scrollTo({ top: 0, behavior: 'smooth' });
   }
 
+  const MIX_EVENT = { notToday: 'not_today', lessLikeThis: 'less_like_this', alwaysHide: 'hide_topic' };
   function applyAction(kind, value) {
     applyPrefAction(kind, value); // updates + persists + syncs to account
+    if (MIX_EVENT[kind]) track(MIX_EVENT[kind]); // emotional-mix signal (no value stored)
     select(selected, true); // re-filter the feed
   }
 
@@ -182,8 +184,11 @@
     }
     if (!repl) {
       flash("That's everything fresh for now — nothing new to swap in.");
+      track('replace_none');
       return;
     }
+    track('replace_used', article.id);
+    if (article.paywalled) track('paywall_replace', article.id);
     dismissed.add(article.id);
     seenIds.add(article.id);
     markDisplayed([repl]);