Add Team Dashboard for cross-device usage aggregation and team comparison

[Copilot]

Implements dashboard view showing personal Copilot usage aggregated across all devices/workspaces, plus team-wide leaderboard for usage comparison. Data sourced from Azure Table Storage (30-day lookback).

Implementation

Backend (extension.ts)

• getDashboardData(): Queries table storage, aggregates entities by userId
• Personal metrics: Sum across machineId/workspaceId for current user
• Team metrics: Group by userId, rank by total tokens
• Cost calculation: Model-aware for personal (via calculateEstimatedCost()), simplified average ($0.05/1M tokens) for team members due to lack of per-user model breakdown in aggregation

Frontend (src/webview/dashboard/)

• Personal summary: tokens, interactions, cost, device/workspace counts, model breakdown
• Team leaderboard: sortable table with rankings, current user highlighting
• Standard webview navigation integration

Navigation

• Command: copilot-token-tracker.showDashboard
• Added btn-dashboard to shared button config
• Message handlers in all existing webviews for cross-navigation

Requirements

• Backend sync configured with Azure Storage Tables
• Table data must include userId dimension
• Valid userId in extension settings

Technical Notes

• Uses BackendUtility.toUtcDayKey() / addDaysUtc() for date range computation
• Accesses backend facade via private property (set during activation)
• Dashboard excludes self-referential navigation button to avoid redundancy

Original prompt

Look at the data we upload to the table storage. Based on what we have there, I want to build a mini dashboarding website on this data, where we can see the the following aspects:

• your own user data summarized across your different editors/devices
• the summarized view across your team so you can compare yourself with your team mates

This dashboard needs to be able to be deployed in a standalone SPA type application, that loads the data from the table storage.

For starters, we'll display this dashboard in a new view in our extension.

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