feat(deploy): add production stack for the VPS

Compose file for ikerdemo.cat with nginx as TLS terminator, the three
.NET services, Zitadel and the storage stack. Values come from
deploy/.env.prod (untracked). Adds the frontend image, the migration
script and the Zitadel provisioning for production.

deploy/scripts/migrate.prod.sh

@@ -0,0 +1,24 @@
+#!/bin/sh
+# Applies EF Core migrations to the prod Postgres, from a throwaway SDK
+# container attached to the compose network (postgres is not published to the host).
+set -eu
+
+DEPLOY_DIR="$(CDPATH= cd -- "$(dirname -- "$0")/.." && pwd)"
+BACKEND_DIR="$(CDPATH= cd -- "$DEPLOY_DIR/../backend" && pwd)"
+ENV_FILE="$DEPLOY_DIR/.env.prod"
+
+. "$ENV_FILE"
+
+NETWORK="musify-prod_default"
+CONN="Host=postgres;Port=5432;Database=${POSTGRES_DB};Username=${POSTGRES_USER};Password=${POSTGRES_PASSWORD}"
+
+docker run --rm \
+  --network "$NETWORK" \
+  -v "$BACKEND_DIR":/src \
+  -w /src/Musify.Infrastructure \
+  mcr.microsoft.com/dotnet/sdk:10.0 \
+  sh -c "dotnet tool install --global dotnet-ef >/dev/null 2>&1 || true; \
+    export PATH=\$PATH:/root/.dotnet/tools; \
+    dotnet restore Musify.Infrastructure.csproj; \
+    dotnet user-secrets set 'Database:ConnectionString' '$CONN' >/dev/null; \
+    dotnet ef database update --context Database"