Feature/v2/filemanager (#4121)

FileManager Component Overview

Purpose: Modal component for selecting and managing PDF files with
preview capabilities

  Architecture:
- Responsive Layouts: MobileLayout.tsx (stacked) vs DesktopLayout.tsx
(3-column)
- Central State: FileManagerContext handles file operations, selection,
and modal state
  - File Storage: IndexedDB persistence with thumbnail caching

  Key Components:
  - FileSourceButtons: Switch between Recent/Local/Drive sources
  - FileListArea: Scrollable file grid with search functionality
- FilePreview: PDF thumbnails with dynamic shadow stacking (1-2 shadow
pages based on file count)
  - FileDetails: File info card with metadata
  - CompactFileDetails: Mobile-optimized file info layout

  File Flow:
1. Users select source → browse/search files → select multiple files →
preview with navigation → open in
  tools
  2. Files persist across tool switches via FileContext integration
  3. Memory management handles large PDFs (up to 100GB+)

 ```mermaid
 graph TD
      FM[FileManager] --> ML[MobileLayout]
      FM --> DL[DesktopLayout]

      ML --> FSB[FileSourceButtons<br/>Recent/Local/Drive]
      ML --> FLA[FileListArea]
      ML --> FD[FileDetails]

      DL --> FSB
      DL --> FLA
      DL --> FD

      FLA --> FLI[FileListItem]
      FD --> FP[FilePreview]
      FD --> CFD[CompactFileDetails]

  ```

---------

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

frontend/src/styles/theme.css

@@ -74,6 +74,9 @@
   --bg-muted: #f3f4f6;
   --bg-background: #f9fafb;
   --bg-toolbar: #ffffff;
+  --bg-file-manager: #F5F6F8;
+  --bg-file-list: #ffffff;
+  --btn-open-file: #0A8BFF;
   --text-primary: #111827;
   --text-secondary: #4b5563;
   --text-muted: #6b7280;
@@ -175,6 +178,9 @@
   --bg-muted: #1F2329;
   --bg-background: #2A2F36;
   --bg-toolbar: #272A2E;
+  --bg-file-manager: #1F2329;
+  --bg-file-list: #2A2F36;
+  --btn-open-file: #0A8BFF;
   --text-primary: #f9fafb;
   --text-secondary: #d1d5db;
   --text-muted: #9ca3af;