Add Azure Storage backend configuration panel to diagnostics

[Copilot]

Diagnostics view lacked visibility into Azure Storage backend configuration and sync status. Users had no way to see configuration state, last sync time, or storage statistics without navigating through settings.

Changes

Extension Core (src/extension.ts)

• Added getBackendStorageInfo() to aggregate backend settings, sync state from global storage, and compute device count from unique workspace IDs
• Extended diagnostics HTML generation to include backend storage info in initial data payload
• Wired message handlers for configureBackend and openSettings commands

Diagnostics Webview (src/webview/diagnostics/main.ts)

• Added "☁️ Azure Storage" tab with renderBackendStoragePanel()
• Implemented three-state UI based on configuration status:
  • Disabled (gray ⚪): Setup guide with requirements
  • Partial (orange ⚠️): Warning that configuration is incomplete
  • Configured (green ✅): Full configuration details, sync stats, and management actions
• Statistics cards show device count (from workspace IDs), local session count, cloud record count, and last sync timestamp
• Configuration details table displays storage account, subscription, resource group, and table names

UI

Backend Disabled

Backend Partially Configured

Backend Fully Configured

Notes

• Cloud record count placeholder shows "—" until Azure Storage query implementation is added
• Device count heuristic: unique workspace IDs extracted from session file paths
• Configuration button falls back to opening settings if backend configuration command isn't registered

Original prompt

Add a button on the diagnostics to trigger the showing of the azure storage screen so it can be configured. Show the button with a color that indicate if the setting have been configured and show the timestamp of the latest sync, with the amount of records in the storage account for the configured users.

Also show the amount of devices and number of sessions per device.

So perhaps this should become a mini panel or table instead of just a button. Make a sensible proposal and add the changes to implement it.

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