feat: add HTTP auth and Sablier scale-to-zero to VERT stack

Added authentication and scale-to-zero capabilities to VERT file converter service:

**Authentication**:
- Added HTTP Basic Auth middleware using VERT_AUTH_USERS
- Auth middleware applied to web-secure router
- Credentials configured via .env file (htpasswd format)

**Sablier Scale-to-Zero**:
- Added sablier.enable and sablier.group labels
- Created proxy/dynamic/vert-sablier.yaml with Sablier middleware config
- 1-hour session duration before automatic scale-down
- Ghost theme with custom display name
- Middleware chain: sablier-vert@file → auth → compress

**Configuration Updates**:
- Added VERT_SABLIER_ENABLED to arty.yml (default: true)
- Updated CLAUDE.md with auth and Sablier documentation
- Middleware order ensures Sablier wakes container before auth check

Infrastructure:
- Follows same pattern as Scrapy service for auth
- Dynamic Traefik configuration for Sablier plugin
- Container name: vert_app (referenced in Sablier config)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

proxy/dynamic/vert-sablier.yaml

@@ -0,0 +1,11 @@
+http:
+  middlewares:
+    sablier-vert:
+      plugin:
+        sablier:
+          names: vert_app
+          sablierUrl: http://sablier_app:10000
+          sessionDuration: 1h
+          dynamic:
+            displayName: VERT File Converter
+            theme: ghost