feat(deploy): consolidated dev stack with auto-provisioned Zitadel

Single docker-compose stack for local development (Postgres, Zitadel,
RabbitMQ, SeaweedFS + bucket init, Jaeger) plus an optional overlay to run
the .NET apps in Docker. up.ps1 orchestrates the full bootstrap: stack up,
stream-ticket keys, EF Core migrations and Zitadel provisioning.

- Zitadel is provisioned automatically (service-account PAT -> project +
  OIDC app with JWT access token); the generated ClientId is wired into
  Musify.Api user-secrets and .env. No manual console steps.
- ZITADEL_EXTERNAL_DOMAIN=host.docker.internal so token validation works
  both with local apps and full-docker.
- App Dockerfiles copy AppSettings*.json to lowercase so config loads on
  case-sensitive Linux; Worker image ships ffmpeg.
- Scripts split by responsibility (common/stream-keys/migrate/provision);
  apps overlay de-duped via YAML anchors.
- Remove the superseded standalone seaweedfs compose; point docs/development
  at the unified stack.

deploy/scripts/common.ps1

@@ -0,0 +1,15 @@
+#requires -Version 5.1
+# Shared helpers for the deploy scripts.
+
+function Write-Step([string]$Message) { Write-Host "`n==> $Message" -ForegroundColor Cyan }
+
+# Parses a .env file into a hashtable (ignores comments and blank lines).
+function Read-DotEnv([string]$Path) {
+    $values = @{}
+    if (Test-Path $Path) {
+        Get-Content $Path | ForEach-Object {
+            if ($_ -match '^\s*([^#=\s][^=]*)=(.*)$') { $values[$matches[1].Trim()] = $matches[2].Trim() }
+        }
+    }
+    return $values
+}