Implement analytics feature

Add server-side visit analytics collection, a public-page ping endpoint,
and a full-screen AnalyticsView for admins.

Backend:
- Add pagerite/analytics.py: Analytics/Visit model, Store, and persistence
- Wire /_a ping endpoint and GET /_api/analytics into pagerite/app.py

Frontend:
- Add full-screen AnalyticsView with visitor charts and transition map
- Add VisitorCharts and TransitionGraph subcomponents
- Add analytics JS helpers in frontend/src/analytics/
- Send navigation pings from frontend/src/pagerite.js
- Mount AnalyticsView from frontend/src/main.js
- Document the feature in docs/analytics.md and update AGENTS.md

frontend/src/analytics/format.js

@@ -0,0 +1,54 @@
+/**
+ * Formatters and aggregators for summary sections: totals and the recent
+ * visit trail.
+ */
+
+/** Total page views across every page and every bucket. */
+export function calcTotalViews(views) {
+  let n = 0
+  for (const buckets of Object.values(views || {})) {
+    for (const c of Object.values(buckets)) n += c
+  }
+  return n
+}
+
+/** Build a path -> page title lookup from the site tree. */
+function buildTitleMap(pageTree) {
+  const titles = new Map()
+  const walk = (items) => {
+    for (const item of items || []) {
+      titles.set(`/${item.path}`, item.title)
+      walk(item.children)
+    }
+  }
+  walk(pageTree)
+  return titles
+}
+
+/** Last path segment for display; front page becomes a house icon. */
+function slugOf(path) {
+  return path === '/' ? '🏠' : path.split('/').pop()
+}
+
+/**
+ * Format recent visits for display, newest first. Each step is a linked slug
+ * pointing to its article; external referers/origins and direct entries are
+ * omitted. The link title shows the article heading when known.
+ */
+export function formatRecentVisits(visits, pageTree, limit = 50) {
+  const titles = buildTitleMap(pageTree)
+  return [...visits]
+    .reverse()
+    .map((v) => ({
+      when: new Date(v.start).toLocaleString(),
+      steps: [v.entry, ...(v.trail || [])]
+        .filter((p) => p?.startsWith('/'))
+        .map((p) => ({
+          path: p,
+          slug: slugOf(p),
+          title: titles.get(p) || '',
+        })),
+    }))
+    .filter((v) => v.steps.length)
+    .slice(0, limit)
+}