Registry and Analytics: run, subnet, direction and protocol filters, successes-by-target chart

Registry (/registry):
- filters by run (slice by the address's cycle in that run), subnet
  (drop-down of configured subnets), direction (egress/ingress) and
  protocol (icmp, tcp, ssh, https, tls); status in scope is computed over
  the narrowed checks
- chart "successful checks per target (egress) / site (ingress)" when both
  direction and protocol are chosen; a row opens the list of addresses
  (dialog, CSV)
- API: direction/protocol parameters and run in GET /admin/registry,
  GET /admin/registry/breakdown and /breakdown/list
- subnet filter passes ids as one JSON parameter (SQLite variable limit)

Analytics (/analytics):
- subnet filter recomputes the whole page over the addresses of the run
  inside the subnet; only their checks are read; cache per run and subnet
- direction and protocol focus the page; with both set the registry chart
  is shown
- subnet parameter in GET /admin/analytics/runs/{id} and lists (JSON, CSV)

Docs: plans and summaries in docs/changes, README, API, USAGE.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/httpapi/routes.go

@@ -64,6 +64,8 @@ func (s *Server) routeTable() []route {
 		{"POST /api/v1/admin/auto-cycle/start", s.handleAdminStartAutoCycle, accessAdmin},
 		{"POST /api/v1/admin/auto-cycle/stop", s.handleAdminStopAutoCycle, accessAdmin},
 		{"GET /api/v1/admin/registry", s.handleAdminRegistry, accessAdmin},
+		{"GET /api/v1/admin/registry/breakdown", s.handleAdminRegistryBreakdown, accessAdmin},
+		{"GET /api/v1/admin/registry/breakdown/list", s.handleAdminRegistryBreakdownList, accessAdmin},
 		{"GET /api/v1/admin/registry/{ip}", s.handleAdminRegistryHistory, accessAdmin},
 		{"GET /api/v1/admin/analytics/runs", s.handleAnalyticsRuns, accessAdmin},
 		{"GET /api/v1/admin/analytics/runs/{id}", s.handleAnalyticsRun, accessAdmin},