Add diagnostic report generation for troubleshooting extension issues

[Copilot]

Users report extension failures without diagnostic context, making troubleshooting difficult. This adds a diagnostic report feature that captures environment state, file discovery results, and aggregated statistics without exposing code or conversation content.

Changes

New Command & UI

• copilot-token-tracker.generateDiagnosticReport command via Command Palette
• "Diagnostics" button in details panel footer
• Webview panel with copy-to-clipboard and GitHub issue link

Report Contents

• Extension/VS Code versions, OS, Node version, environment (Codespaces/Remote/Local)
• Copilot extension status and versions (attempts tier detection via API)
• Session file locations (first 20) with sizes and timestamps - no content
• Token statistics: today/month totals, model breakdown, sessions, interactions
• Cache hit/miss rates

Implementation

• Async file stat operations (Promise.all) to avoid blocking
• Repository URL helper method to centralize GitHub links
• Structured status display instead of raw JSON dump

Example Report Output

## Session Files Discovery
Total Session Files Found: 15

Session File Locations (first 20):
  1. /home/user/.config/Code/User/workspaceStorage/.../session1.json
     - Size: 12458 bytes
     - Modified: 2026-01-06T14:30:00.000Z

## Token Usage Statistics
### Today
  - Total Tokens: 12,458
  - Sessions: 5
  - Models Used:
    * gpt-4o: 8,234 tokens (↑4,117 ↓4,117)
    * claude-sonnet-3.5: 4,224 tokens (↑2,112 ↓2,112)

Report contains only file metadata and aggregated statistics - safe for public sharing.

Original prompt

Sometimes users report that the extension does not work. Add a way to report back the logs from the output panel for the extension and let the user either directly add that to an issue in GitHub or share privately

I want to see the files we found (only their locations), if we found matching json files, and what we pulled out of them in terms of tokens, models, sessions and such. If possible, report if this is a copilot free/pro/pro+/business/enterprise user or not. Add information about extension version, VS Code version, OS, and perhaps other things you can think of.

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