Added structure for filemanager (#4078)

Overview

Replaced scattered file inputs with a unified modal-based upload system.
Users now upload files via a global Files button with intelligent
tool-aware filtering.

  Key Changes

  🔄 New Upload Flow

  - Before: Direct file inputs throughout the UI
- After: Single Files button → Modal → Tool filters files automatically

  🎯 Smart File Filtering

  - Modal shows only supported file types based on selected tool
  - Visual indicators for unsupported files (grayed out + badges)
  - Automatic duplicate detection

  ✨ Enhanced UX

  - Files button shows active state when modal is open
  - Consistent upload experience across all tools
  - Professional modal workflow

  Architecture

  New Components

  FilesModalProvider → FileUploadModal → Tool-aware filtering

  Button System Redesign

  type: 'navigation' | 'modal' | 'action'
  // Only navigation buttons stay active
  // Modal buttons show active when modal open

  Files Changed

  - ✅ QuickAccessBar.tsx - Added Files button
  - ✅ FileUploadModal.tsx - New tool-aware modal
  - ✅ HomePage.tsx - Integrated modal system
  - ✅ ConvertE2E.spec.ts - Updated tests for modal workflow

  Benefits

  - Unified UX: One place to upload files
  - Smart Filtering: Only see relevant file types
  - Better Architecture: Clean separation of concerns
  - Improved Testing: Reliable test automation

Migration: File uploads now go through Files button → modal instead of
direct inputs. All existing functionality preserved.

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Co-authored-by: Connor Yoh <connor@stirlingpdf.com>