Add authentication: admin/agent bearer tokens for the API, login for the dashboard

control-api: every route now carries a mandatory access level (admin / agent /
open) in a route table. All /api/v1/admin/* require the admin token; the
write calls of validator-agent and prober (self-check, events, results,
complete) require a separate static agent token; register, heartbeat and
fetching the assignment stay open. Tokens come from env vars, are compared in
constant time and never logged. An empty token leaves that level open with a
startup warning (backward compatible).

validator-agent / prober: apiclient sends the agent token only to control-api.

admin-dashboard: login/password (from env) with a stateless HMAC session
cookie, Origin-based CSRF check, per-IP brute-force throttle, HX-Redirect for
htmx polls, logout in the sidebar; the dashboard calls control-api with the
admin token. Login page layout fixed after review.

Also: env plumbing in docker-compose/rxprod-compose/systemd/config examples,
e2e script with token assertions, tests, docs (API, SETUP, USAGE, DASHBOARD,
README), plan and review under docs/changes/, bin/ rebuilt with new
SHA256SUMS.

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

internal/dashboard/handlers_ips.go

@@ -25,7 +25,7 @@ func (s *Server) handleIPsPage(w http.ResponseWriter, r *http.Request) {
 	data := ipsPageData{Items: items, FIPSettleSeconds: settings.FIPSettleSeconds}
 	data.ActiveNav = "ips"
 	data.Banner = bannerFor(err)
-	s.renderPage(w, "ips_page", data)
+	s.renderPage(w, r, "ips_page", data)
 }
 
 func (s *Server) handleIPDetail(w http.ResponseWriter, r *http.Request) {
@@ -34,7 +34,7 @@ func (s *Server) handleIPDetail(w http.ResponseWriter, r *http.Request) {
 	data := ipDetailData{Detail: detail}
 	data.ActiveNav = "ips"
 	data.Banner = bannerFor(err)
-	s.renderPage(w, "ip_detail_page", data)
+	s.renderPage(w, r, "ip_detail_page", data)
 }
 
 // renderIPsTable re-fetches the current queue and renders the ips_table