feat: Add comprehensive plugin documentation and advanced template system

Added complete plugin documentation with visual mockups and expanded template
variable system with CONTEXT, DATE helpers, and default values.

Backend Changes:
- Extended template_parser.py to support all new template types
- Added PROMPT with default values: {{PROMPT:var|desc|default}}
- Added CONTEXT variables: {{CONTEXT:business_name}}, {{CONTEXT:owner_email}}
- Added DATE helpers: {{DATE:today}}, {{DATE:+7d}}, {{DATE:monday}}
- Implemented date expression evaluation for relative dates
- Updated compile_template to handle all template types
- Added context parameter for business data auto-fill

Frontend Changes:
- Created comprehensive HelpPluginDocs.tsx with Stripe-style API docs
- Added visual mockup of plugin configuration form
- Documented all template types with examples and benefits
- Added Command Reference section with allowed/blocked Python commands
- Documented all HTTP methods (GET, POST, PUT, PATCH, DELETE)
- Added URL whitelisting requirements and approval process
- Created Platform Staff management page with edit modal
- Added can_approve_plugins and can_whitelist_urls permissions

Platform Staff Features:
- List all platform_manager and platform_support users
- Edit user details with role-based permissions
- Superusers can edit anyone
- Platform managers can only edit platform_support users
- Permission cascade: users can only grant permissions they have
- Real-time updates via React Query cache invalidation

Documentation Highlights:
- 4 template types: PROMPT, CONTEXT, DATE, and automatic validation
- Visual form mockup showing exactly what users see
- All allowed control flow (if/elif/else, for, while, try/except, etc.)
- All allowed built-in functions (len, range, min, max, etc.)
- All blocked operations (import, exec, eval, class/function defs)
- Complete HTTP API reference with examples
- URL whitelisting process: contact pluginaccess@smoothschedule.com

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

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

smoothschedule/platform_admin/serializers.py

@@ -234,9 +234,9 @@ class PlatformUserSerializer(serializers.ModelSerializer):
         model = User
         fields = [
             'id', 'email', 'username', 'first_name', 'last_name', 'full_name', 'role',
-            'is_active', 'is_staff', 'is_superuser',
+            'is_active', 'is_staff', 'is_superuser', 'permissions',
             'business', 'business_name', 'business_subdomain',
-            'date_joined', 'last_login'
+            'date_joined', 'last_login', 'created_at'
         ]
         read_only_fields = fields