Fix Team Dashboard slow initial render by caching last fetch result

[Copilot]

Every time the Team Dashboard opened, it blocked on a full backend fetch + local maturity score calculation before rendering anything, making the panel feel unresponsive.

Changes

• Cache getDashboardData() result in a new lastDashboardData property, mirroring the existing pattern for lastDetailedStats, lastDailyStats, and lastUsageAnalysisStats.
• Render immediately from cache — if lastDashboardData is populated, it is posted to the webview right after panel creation, before the background fetch completes.
• Background refresh — fresh data is always fetched after opening; the webview updates silently when it arrives.
• Fallback-aware error handling — the error state is only shown when there is no cached data to display; if the refresh fails but a previous result exists, the stale data remains visible.
• Cache invalidation — lastDashboardData is cleared together with the other stat caches on explicit cache clear.
• Refresh caches too — refreshDashboardPanel() now writes the new result to lastDashboardData.

// If we have cached data, show it immediately so the panel renders fast
if (this.lastDashboardData) {
  this.dashboardPanel.webview.postMessage({
    command: "dashboardData",
    data: this.lastDashboardData,
  });
}

// Fetch fresh data in the background; update cache and webview when done
const dashboardData = await this.getDashboardData();
this.lastDashboardData = dashboardData;
this.dashboardPanel?.webview.postMessage({ command: "dashboardData", data: dashboardData });

Original prompt

Currently the team Dashboard, does not low pretty Quickly. It seems like it do a full scan or refresh or something before it's Starts to show. so you have the klik on the button and wait for quit a while. Look at this Behaviour en implement a fix.

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