Improve backend sync and team dashboard

[rajbos]

This pull request introduces improvements to backend sync logging, defers the start of the backend sync timer until after initial token analysis, and enhances the dashboard with more detailed team data, including the date range of available statistics. The changes improve both the robustness of backend operations and the transparency of team data in the dashboard UI.

Backend Sync Improvements:

• Added detailed logging to clarify why backend sync timers are not started or are skipped, including whether cloud sync is disabled or the backend is not configured (src/backend/services/syncService.ts). [1] [2]
• The backend sync timer interval is now always set to the minimum interval, and the log message now includes the interval in minutes for clarity (src/backend/services/syncService.ts).
• Added warnings and timestamp updates when backend credentials are unavailable, making failures more visible and preventing stale "last sync" displays (src/backend/services/syncService.ts).

Extension Startup and Sync Coordination:

• The backend sync timer is now started only after the initial token analysis completes, reducing resource contention during startup. This is coordinated via the new startBackendSyncAfterInitialAnalysis method in CopilotTokenTracker (src/extension.ts). [1] [2] [3]

Dashboard Data and UI Enhancements:

• The dashboard now tracks and displays the first and last dates of available team data, providing more context about the data range. This includes changes to both the backend data aggregation and the webview UI (src/extension.ts, src/webview/dashboard/main.ts). [1] [2] [3] [4] [5] [6] [7]
• Added console logging for dashboard data received and for backend storage info retrieval, aiding in debugging and transparency (src/extension.ts, src/webview/dashboard/main.ts). [1] [2] [3]
• Added a warning in the diagnostics webview if backend storage info is missing, making diagnostics more robust (src/webview/diagnostics/main.ts).