feat(forte-drop): wildcard IngressRoute for per-slug drop subdomains

No forte-helm chart change needed after all. The forteapp chart emits one exact
Host(`drop.forteapps.net`) route (apex: admin + /api + public /shared). Add an
ADDITIVE standalone IngressRoute for the per-slug wildcard *.drop.forteapps.net,
pointing at the SAME chart service (forte-drop-app:3000 — whose targetPort is the
auth sidecar when auth is on), so forte drop subdomains flow through the sidecar and
are Forte-login gated exactly like the admin root.

priority:1 (LOW) is load-bearing: Traefik orders routers by rule-length by default,
and this regex is longer than Host(`mcp.drop.forteapps.net`) — without the explicit
low priority it would STEAL mcp.drop (and apex) traffic into the web pod. priority:1
guarantees the exact Host() routers (mcp release + chart apex) always win.

Traefik v3 (chart 28.x) HostRegexp = Go RE2; verify the rendered router against
mcp./www./app./apex/<real-slug> before prod. Uses the wildcard-drop-forteapps-net-tls
secret from the Certificate added in the same branch.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/overlays/upc-dev/forte-drop/kustomization.yaml

@@ -6,3 +6,4 @@ resources:
 - forte-drop-pdb.yaml
 - forte-drop-secrets-sealed.yaml
 - wildcard-drop-tls-certificate.yaml
+- forte-drop-subdomains-ingressroute.yaml