feat(settings): CA generation from the UI; Routstr panel beside the API key

WebUI RULE (operator, 2026-08-14): never point users at a terminal. The
certificate section told users to run setup-node-ca.sh by hand — it now
has a Generate button backed by system.node-ca.generate, which runs the
idempotent script server-side (live-tested: generated and /ca.crt serves).
Routstr budget panel moves directly under the Claude API key card.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

core/archipelago/src/api/rpc/dispatcher.rs

@@ -503,6 +503,7 @@ impl RpcHandler {
             "ai.permissions.set" => self.handle_ai_permissions_set(params).await,
             "system.settings.get" => self.handle_system_settings_get(params).await,
             "system.settings.set" => self.handle_system_settings_set(params).await,
+            "system.node-ca.generate" => self.handle_system_node_ca_generate().await,
             "system.kiosk-display.get" => self.handle_system_kiosk_display_get().await,
             "system.kiosk-display.set" => self.handle_system_kiosk_display_set(params).await,