feat: Add filter persistence with settings integration

[michelroegl-brunner]

🎯 Feature: Filter Persistence System

This PR introduces a comprehensive filter persistence system that allows users to save and restore their script filter preferences across sessions.

✨ Key Features

🔧 Settings Integration

• New toggle in General Settings to enable/disable filter persistence
• Visual indicator when filters are being saved automatically
• Settings modal shows current saved filter status and details

💾 Persistent Storage

• Saves complete filter state to FILTERS variable in .env file
• Includes search query, type filters, sort order, and updatable status
• JSON-based storage for easy parsing and validation

⚡ Smart Auto-Save

• Automatically saves filters when changed (with 500ms debounce)
• Only saves when persistence is enabled
• Graceful error handling and user feedback

🔄 Seamless Restoration

• Loads saved filters on page load when persistence is enabled
• Falls back to defaults when persistence is disabled
• Loading states during filter restoration

📱 Enhanced UX

• Loading spinner while restoring filters
• Status indicator showing auto-save is active
• Clear saved filters option in settings
• Works across all script tabs (Available, Downloaded, Installed)

🛠️ Technical Implementation

API Endpoints

• POST /api/settings/filters - Save current filters
• GET /api/settings/filters - Retrieve saved filters
• DELETE /api/settings/filters - Clear saved filters

Components Updated

• FilterBar - Added persistence props and loading states
• ScriptsGrid - Integrated filter loading/saving logic
• DownloadedScriptsTab - Added persistence support
• GeneralSettingsModal - Added filter management UI

Data Flow

1. User toggles persistence in settings
2. Filters auto-save to .env when changed
3. Page loads restore saved filters if enabled
4. Settings show current filter status

🎨 User Experience

• When enabled: Filters persist across page reloads and sessions
• When disabled: Uses default filters, no persistence
• Visual feedback: Clear indicators for loading and auto-save status
• Settings management: Easy toggle and filter clearing

This enhancement significantly improves user experience by maintaining their preferred filter settings, reducing the need to reconfigure filters on each visit.