hub v0.31.0: accept 'critical' severity at event ingest + UI badges/CSS; event_test.go (red-proofed); REUSE.md §1/§3 updated

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PSK5g6qYLknKj8u3QAFEr6

hub/internal/web/templates/customer_unified.html

@@ -488,6 +488,7 @@
         <section class="card">
             <h2>Events
                 {{if .EventCounts}}
+                    {{with mapGet .EventCounts "critical"}}<span class="severity-badge severity-critical">{{.}} critical</span>{{end}}
                     {{with mapGet .EventCounts "error"}}<span class="severity-badge severity-error">{{.}} error{{if gt . 1}}s{{end}}</span>{{end}}
                     {{with mapGet .EventCounts "warning"}}<span class="severity-badge severity-warning">{{.}} warning{{if gt . 1}}s{{end}}</span>{{end}}
                 {{end}}