VS Code extension: add on-demand Account & Usage panel access

Feature Request

Is your feature request related to a problem?

Currently, the Account & Usage panel (showing session %, weekly %, plan details) in the VS Code extension only appears automatically when usage reaches ~90%. There's no way to open it on demand to check current usage levels.

Describe the solution you'd like

A way to open the Account & Usage panel at any time — for example:

• A clickable status bar item showing current usage %
• A command palette entry ("Claude Code: Show Usage")
• A keyboard shortcut
• A /usage slash command that shows the full panel (not just context window info)

Describe alternatives you've considered

• Using the CLI (claude /cost) — but this requires leaving the IDE
• Checking usage on claude.ai web — also requires leaving the IDE
• Waiting for the 90% warning — too late to plan work around limits

Additional context

When working on larger tasks, it's useful to check remaining capacity mid-session to decide whether to continue or pause. Having this info accessible on demand (like most subscription-based tools provide) would be a quality-of-life improvement.