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>

frontend/src/components/Sidebar.tsx

@@ -17,7 +17,8 @@ import {
   ChevronDown,
   BookOpen,
   FileQuestion,
-  LifeBuoy
+  LifeBuoy,
+  Zap
 } from 'lucide-react';
 import { Business, User } from '../types';
 import { useLogout } from '../hooks/useAuth';
@@ -215,14 +216,24 @@ const Sidebar: React.FC<SidebarProps> = ({ business, user, isCollapsed, toggleCo
                     <span>{t('nav.ticketingHelp', 'Ticketing System')}</span>
                   </Link>
                   {role === 'owner' && (
-                    <Link
-                      to="/help/api"
-                      className={`flex items-center gap-3 py-2 text-sm font-medium rounded-lg transition-colors px-3 ${location.pathname === '/help/api' ? 'bg-white/10 text-white' : 'text-white/60 hover:text-white hover:bg-white/5'}`}
-                      title={t('nav.apiDocs', 'API Documentation')}
-                    >
-                      <Code size={16} className="shrink-0" />
-                      <span>{t('nav.apiDocs', 'API Docs')}</span>
-                    </Link>
+                    <>
+                      <Link
+                        to="/help/api"
+                        className={`flex items-center gap-3 py-2 text-sm font-medium rounded-lg transition-colors px-3 ${location.pathname === '/help/api' ? 'bg-white/10 text-white' : 'text-white/60 hover:text-white hover:bg-white/5'}`}
+                        title={t('nav.apiDocs', 'API Documentation')}
+                      >
+                        <Code size={16} className="shrink-0" />
+                        <span>{t('nav.apiDocs', 'API Docs')}</span>
+                      </Link>
+                      <Link
+                        to="/help/plugins"
+                        className={`flex items-center gap-3 py-2 text-sm font-medium rounded-lg transition-colors px-3 ${location.pathname === '/help/plugins' ? 'bg-white/10 text-white' : 'text-white/60 hover:text-white hover:bg-white/5'}`}
+                        title={t('nav.pluginDocs', 'Automation Plugins')}
+                      >
+                        <Zap size={16} className="shrink-0" />
+                        <span>{t('nav.pluginDocs', 'Plugin Docs')}</span>
+                      </Link>
+                    </>
                   )}
                   <div className="pt-2 mt-2 border-t border-white/10">
                     <Link