refact: screenshot settings folder

[florent37]

Summary

Refactor screenshot & screen recording workflows and add configurable document storage support in Settings.
Users can now customize the destination folder for screenshots, screen records, and exported files via a dedicated General tab in Settings, falling back to ~/Documents/Flocon by default.

🚀 Key Changes

1. Configurable Flocon Documents Directory

• Custom Location: Added support for configuring a custom FloconDocuments folder path instead of a hardcoded path.
• Default Fallback: Automatically defaults to ~/Documents/Flocon if no custom path has been specified.
• Persistence: Saved across sessions using SettingsRepository & SettingsDataSourcePrefs (flocon_documents_path key).
• Domain Integration: Updated GetFloconDocumentPathUseCase to retrieve the configured path from SettingsRepository.

2. Native Folder Picker in Settings UI

• Added a new General settings tab in SettingsScreen.
• Displayed the current folder path in a styled text field with:
  • Pick... button on the right: opens a native folder selection dialog (FolderPicker, using native macOS FileDialog for directory mode and JFileChooser fallback on other platforms).
  • Save: explicitly saves manual path input.
  • Reset to default: reverts path back to ~/Documents/Flocon.
  • Open Folder: opens the folder directly in Finder / File Explorer.

3. Screenshot & Screen Recording Refactoring

• Extracted and centralized screenshot and video recording logic into dedicated domain use cases (TakeScreenshotUseCase, StartRecordingVideoUseCase, StopRecordingVideoUseCase).
• Connected screenshot / recording outputs and top bar actions to GetFloconDocumentPathUseCase.

🧪 Testing

• Unit Tests: Added GetFloconDocumentPathUseCaseTest verifying fallback to default path when unset/blank and properly returning user-configured paths.
• Directory Picker: Verified native directory picker opens and correctly sets the absolute directory path.
• Persistence: Verified custom directory is retained across app restarts.
• Screenshot / Record: Captured screenshots and confirmed files are saved into <FloconDocuments>/Screenshot.