Add observable query diagnostics page

[Copilot]

Adds a live Query Diagnostics tab to the Lens popup that surfaces real-time observable query state from the inspected Arc application via ArcContext.observableQueryDiagnostics.

Approach

The diagnostics object lives inside the Arc application's React fiber tree. Rather than a WebSocket bridge, the extension injects a page-world script (same technique as Arc context detection) that traverses the fiber, finds the ArcContext provider node, and calls observableQueryDiagnostics.getSnapshot() — returning a plain serializable object over the structured-clone boundary.

// Injected into page world via chrome.scripting.executeScript
if (isArcContextValue(contextValue)) {
    const diag = contextValue.observableQueryDiagnostics;
    if (diag && typeof diag.getSnapshot === 'function') {
        return diag.getSnapshot();   // ObservableQueryDiagnosticsSnapshot
    }
}

The popup polls this every 2 seconds for live updates.

Changes

• @cratis/arc.react — bumped to ^20.28.0
• arc-context.ts — adds captureObservableQueryDiagnosticsFromPage (page-world injected fn) and captureObservableQueryDiagnosticsForActiveTab (extension-side async API); re-exports all snapshot sub-types from @cratis/arc/queries
• storage.ts — adds 'observable-query-diagnostics' to PopupTab
• ObservableQueryDiagnosticsView.tsx (new) — polls every 2 s; renders Health, Transport, Multiplexer (with per-connection breakdown), Cache (with per-entry subscriber/listener/size detail), and Ownership sections; tab is disabled when the active page is not an Arc application
• lens-popup.css — oqd-* styles for the diagnostics layout
• LensPopup.tsx — registers the new pi-chart-line tab, disabled when !hasArcContext