Add persistent usage/limits indicator to VS Code status bar

It would be helpful to have a badge or icon in the VS Code status bar (or sidebar) showing current plan usage (e.g., messages remaining, usage percentage).

Currently the only way to check is via the /usage command, which requires manual action. A persistent indicator would help users track their limits without interrupting their workflow.

Possible approaches:

• A status bar item showing remaining messages or a percentage
• A small progress ring/badge on the existing "✱ Claude Code" status bar icon
• A color change on the status bar item as usage approaches the limit