feat(cuprate-ui): companion dashboard for the Cuprate Monero node

Same companion shape as bitcoin-ui/electrs-ui: host-networked nginx
bound to 127.0.0.1:18091 (auth: gated + session_passthrough), serving
a dark glass status page that polls the node's restricted RPC via a
session-gated /cuprate-rpc/ proxy — sync height/target with progress
bar, peers, mempool, chain size and free disk (from get_info), plus a
wallet 'remote node' endpoint. The offline state explains the disk gate
so a refused node says why.

No secret rendering: the restricted RPC is Monero's safe-for-public
subset, so nginx.conf is baked into the image (no pre_start hook, no
bind mount). companion.rs auto-provisions archy-cuprate-ui alongside
cuprate and reaps it when cuprate goes.

Catalog regenerated (cuprate-ui entry + manifest embed, 18091 into the
mesh launch-port list). NOTE: releases/app-catalog.json is UNSIGNED as
committed — run scripts/sign-catalog.sh before publishing.

core/archipelago/src/health_monitor.rs

@@ -53,8 +53,8 @@ fn container_tier(name: &str) -> StartupTier {
         | "indeedhub-api" => StartupTier::DependentService,
 
         // Tier 4: Frontend/UI
-        "mempool-web" | "bitcoin-ui" | "lnd-ui" | "electrs-ui" | "penpot-frontend"
-        | "penpot-exporter" | "indeedhub" => StartupTier::Frontend,
+        "mempool-web" | "bitcoin-ui" | "lnd-ui" | "electrs-ui" | "cuprate-ui"
+        | "penpot-frontend" | "penpot-exporter" | "indeedhub" => StartupTier::Frontend,
 
         // Tier 3: Application layer (everything else)
         _ => StartupTier::Application,