add insta2spotify stack: namespace, ESO, NFS, 2-container deploy, split ingress

- Namespace insta2spotify (tier 4-aux)
- ExternalSecret from Vault secret/insta2spotify
- NFS volume at /mnt/main/insta2spotify for SQLite + Spotify cache
- Frontend (128Mi) + backend (512Mi req / 2Gi limit) in one pod
- Split ingress: protected (Authentik) for frontend, unprotected for /api/*
- DNS via Cloudflare (proxied)

stacks/insta2spotify/tiers.tf

@@ -0,0 +1,10 @@
+# Generated by Terragrunt. Sig: nIlQXj57tbuaRZEa
+locals {
+  tiers = {
+    core    = "0-core"
+    cluster = "1-cluster"
+    gpu     = "2-gpu"
+    edge    = "3-edge"
+    aux     = "4-aux"
+  }
+}