Add public PageView tracking for portal analytics (#4)

## Summary
Closes #3.

- Add `PageView` model + migration for successful public marketing GET hits
- Wire `PublicPageViewMiddleware` (skips portal/admin/accounts/api/static/health/etc.; fails soft on DB errors)
- Portal analytics report: last-30-day views + top pages table
- Admin registration and tests

## Test plan
- [ ] Apply migration `analytics.0002_pageview`
- [ ] Hit `/` and `/about/` → rows in `PageView` / admin
- [ ] Hit `/healthz/`, `/portal/`, `/admin/` → no new pageviews
- [ ] Open portal Analytics → views count + Top pages look right
- [ ] `uv run python site/manage.py test analytics.tests`

Reviewed-on: #4

site/analytics/admin.py

@@ -1,6 +1,15 @@
 from django.contrib import admin
 
-from analytics.models import Attribution, UTMVisit
+from analytics.models import Attribution, PageView, UTMVisit
+
+
+@admin.register(PageView)
+class PageViewAdmin(admin.ModelAdmin):
+    list_display = ("path", "created_at")
+    list_filter = ("created_at",)
+    search_fields = ("path",)
+    date_hierarchy = "created_at"
+    readonly_fields = ("id", "path", "created_at", "updated_at")
 
 
 @admin.register(UTMVisit)