Add cross-site improvements across three phases

Phase 1 — Quick wins:
- Image lazy-loading on series/resource cards
- Newsletter signup added to Episodes page (before highlights)
- Per-route meta tags via usePageMeta hook (title, og:title, og:description)
- Breadcrumbs on study index, section, and notes pages
- SVG completion checkmark badges on study section list
- Analytics time-range filter (7d / 30d / 90d) in admin panel

Phase 2 — Medium features:
- Related episodes on archived series detail pages
- Resource library two-tier filter (type + tag chips)
- Global search (Fuse.js) moved below sticky header as full-width bar
- Q&A anonymous upvoting with localStorage dedup + admin pin/unpin
- Study enrollment funnel tracking (firstVisitAt, firstCompletionAt) with funnel chart in analytics

Phase 3 — Larger features:
- Study section comments (auto-approve for enrolled users, admin moderation panel)
- Study completion certificate (canvas render, PNG download, shareable public URL)
- Episode script full-text search (mammoth docx extraction, server-side search, admin upload UI)
- Reflection questions renamed from Discussion Questions; quiz answers can be shared to section discussion
- Public certificate route at /certificate/:token with og meta tags
- Comment moderation panel added to admin under Manage > Study Comments

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/Breadcrumbs.tsx

@@ -0,0 +1,36 @@
+import { Link } from 'react-router-dom'
+
+export interface BreadcrumbItem {
+  label: string
+  href?: string
+}
+
+export function Breadcrumbs({ items }: { items: BreadcrumbItem[] }) {
+  if (items.length === 0) return null
+
+  return (
+    <nav aria-label="Breadcrumb" className="study-breadcrumbs">
+      <ol className="study-breadcrumbs-list">
+        {items.map((item, idx) => {
+          const isLast = idx === items.length - 1
+          return (
+            <li key={idx} className="study-breadcrumbs-item">
+              {!isLast && item.href ? (
+                <Link to={item.href} className="study-breadcrumbs-link">
+                  {item.label}
+                </Link>
+              ) : (
+                <span className="study-breadcrumbs-current" aria-current={isLast ? 'page' : undefined}>
+                  {item.label}
+                </span>
+              )}
+              {!isLast && (
+                <span className="study-breadcrumbs-sep" aria-hidden="true"> › </span>
+              )}
+            </li>
+          )
+        })}
+      </ol>
+    </nav>
+  )
+}