fix: implement missing UI features (file picker, color preview, filters, bulk ops)

[Sumit6307]

Description

This PR completes all incomplete TODO items flagged by mentors in issue #1. It implements missing UI functionality for plugin configuration, job management, and plugin operations.

Changes Made

1. File Picker Implementation (ConfigurationField.kt)

• ✅ Implemented Android file picker using ActivityResultContracts.GetContent()
• Users can now browse and select files for FILE-type configuration fields
• Selected file URI is properly stored in plugin configuration

2. Color Picker Enhancement (ConfigurationField.kt)

• ✅ Added parseHexColor() function to parse hex color strings (#RRGGBB)
• Color preview box now updates in real-time as users type
• Proper error handling for invalid color formats (defaults to gray)

3. Job Filtering Feature (JobManagementScreen.kt)

• ✅ Implemented comprehensive filtering dialog with:
  • Job state filter (multi-select checkboxes for all states)
  • Document format filter (dropdown with available formats)
  • User name filter (text input)
  • Job name filter (text input)
• Filter indicator shows when filters are active
• Shows appropriate "No jobs match filters" message when applicable

4. Bulk Plugin Operations (PluginManagementScreen.kt)

• ✅ Added bulk operations menu with:
  • Select All / Deselect All functionality
  • Load Selected plugins (batch operation)
  • Unload Selected plugins (batch operation)
• Checkboxes on plugin cards for multi-selection
• Visual feedback for selected plugins (highlighted background)
• Toast notifications for bulk operations

Testing

• ✅ All features tested and working
• ✅ No linter errors
• ✅ Proper error handling implemented
• ✅ UI follows Material Design 3 guidelines
• ✅ State management properly implemented using Compose state

Related Issue

Fixes #1 - Completes all incomplete TODO items from mentor feedback

Screenshots (if applicable)

[You can add screenshots here showing the new features]

Checklist

• Code follows project style guidelines
• Self-review completed
• Comments added for complex logic
• Documentation updated (if needed)
• No new warnings generated
• Tests pass (if applicable)
• All TODO items resolved