Add dual user classes: admin + tech users with PIN login

- Add tech user management (JSON-backed CRUD with PIN auth)
- Dual login: tabbed Tech Login (username+PIN) / Admin Login (NC credentials)
- Admin panel: tappable user list with detail modal (enable/disable, reset PIN, reset NC password, delete)
- Auto-provision Nextcloud accounts for tech users
- Admin guard: tech users redirected away from admin panel
- New data volume for persistent tech_users.json storage

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

config.py

@@ -4,7 +4,10 @@ class Config:
     """Application configuration loaded from environment variables."""
     SECRET_KEY = os.environ.get('SECRET_KEY', 'dev-secret-key-change-in-production')
     NEXTCLOUD_URL = os.environ.get('NEXTCLOUD_URL', 'https://nextcloud.sdanywhere.com')
-    
+
+    # Tech users JSON file
+    TECH_USERS_FILE = os.environ.get('TECH_USERS_FILE', '/app/data/tech_users.json')
+
     # Session configuration
     SESSION_TYPE = 'filesystem'
     SESSION_FILE_DIR = '/tmp/flask_session'
@@ -13,10 +16,10 @@ class Config:
     SESSION_COOKIE_SAMESITE = 'Strict'
     SESSION_COOKIE_HTTPONLY = True
     SESSION_COOKIE_SECURE = True  # Set to False for local development
-    
+
     # Upload configuration
     MAX_CONTENT_LENGTH = 50 * 1024 * 1024  # 50MB max upload
-    
+
     # Development mode
     DEBUG = os.environ.get('FLASK_DEBUG', 'False').lower() == 'true'
 
@@ -28,7 +31,7 @@ class DevelopmentConfig(Config):
 class ProductionConfig(Config):
     """Production-specific configuration."""
     DEBUG = False
-    
+
     # Ensure these are set in production
     def __init__(self):
         super().__init__()