Speedtest visualization in a lightweight webview

[EhabY]

Follow-up to AIGOV-193.

After running coder speedtest, the user currently sees raw JSON in a text document. We should offer a visual chart as an alternative.

Flow

1. Speed test runs with progress indicator (unchanged).
2. On completion, prompt the user: "View Chart" / "View JSON".
3. "View JSON" opens the raw JSON in a text document (current behavior).
4. "View Chart" opens a webview panel with a throughput chart and summary.

Webview

A new packages/speedtest/ package:

• Vanilla TS + Chart.js only. No React, no framework. Keeps the bundle small.
• Its own minimal Vite config (does not reuse createWebviewConfig since that bakes in React).
• Bundled into dist/webviews/speedtest/.

The webview shows:

• A line chart of throughput (Mbps) over time intervals
• A summary section with total throughput, duration, and direction
• "Copy JSON" and "Save to File" buttons

Extension side

A panel provider or factory function in src/webviews/speedtest/ that creates a WebviewPanel, posts the JSON data via postMessage, and handles copy/save actions.

Files to create/change

• packages/speedtest/ - new package (vite config, src/index.ts, src/index.css)
• src/webviews/speedtest/ - panel provider
• src/commands.ts - modify speedTest to prompt and optionally open webview
• package.json - build script additions

Part of AIGOV-193.