Add Google Drive and OneDrive sync providers with OAuth 2.0 authentication

[Copilot]

Adds Google Drive and OneDrive as sync service providers following the existing WebDAV pattern. Implements OAuth 2.0 with PKCE through modal webview for authentication.

Implementation

6 New Sync Services (Data/Image/PDF variants):

• GoogleDriveDataSyncService, GoogleDriveImageSyncService, GoogleDrivePDFSyncService
• OneDriveDataSyncService, OneDriveImageSyncService, OneDrivePDFSyncService
• Registered in SERVICES_TYPE_MAP and SYNC_TYPES

OAuth Infrastructure:

• OAuthHelper.ts - OAuth 2.0 flow with PKCE, token refresh, secure storage
• OAuthWebViewModal.svelte - Modal webview intercepts redirect URI with auth code
• OAuthSettingsView.svelte - Reusable authentication UI component

Provider APIs:

• GoogleDrive.ts - Drive API v3 wrapper (multipart upload, folder ops, file CRUD)
• OneDrive.ts - Microsoft Graph API wrapper (simple upload, item navigation)

UI Integration:

• GoogleDriveDataSyncSettings.svelte - Settings screen with OAuth flow
• Updated SyncListSettings.svelte to handle new service types
• Added service titles and colors in sync.ts

Architecture

Follows existing patterns:

export class GoogleDriveDataSyncService extends BaseDataSyncService {
    private get tokens(): OAuthTokens {
        return { accessToken: this.accessToken, refreshToken: this.refreshToken, expiresAt: this.expiresAt };
    }
    
    override async ensureRemoteFolder() {
        this.remoteFolderId = await getOrCreateFolder(this.tokens, this.remoteFolder);
    }
    
    override async addDocumentToRemote(document: OCRDocument) {
        await this.sendFolderToRemote(docFolder, document.id);
        await this.putFileContentsFromData(path.join(document.id, DOCUMENT_DATA_FILENAME), document.toString());
        await this.createValidMarker(document.id);
    }
}

Uses existing dependencies only:

• @nativescript-community/ui-webview for OAuth modal
• @nativescript-community/https for API requests

Configuration Required

⚠️ OAuth client IDs are placeholders - users must create their own OAuth applications:

Google Drive: Update GOOGLE_DRIVE_PROVIDER.config.clientId in GoogleDrive.ts
OneDrive: Update ONEDRIVE_PROVIDER.config.clientId in OneDrive.ts

See CLOUD_SYNC_SETUP.md for credential setup instructions.

Limitations

• Simple upload only (no resumable for large files >4MB)
• No rate limiting or exponential backoff
• Basic conflict resolution (newer overwrites)
• Requires OAuth app configuration per deployment

Files Changed

18 files, 2,544 lines added:

• 11 new service/helper files
• 4 new UI components
• 3 documentation files

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