Show OpenRouter and DeepSeek balances in the menu bar

[giuseppebisemi]

Summary

• show OpenRouter's remaining credit balance in the menu bar instead of its usage percent
• show DeepSeek's available credit balance in the menu bar instead of the synthetic 0% usage value
• make DeepSeek's menu bar metric settings balance-only and crop the DeepSeek icon viewBox so it renders larger
• add a leading spacer before menu bar text labels so provider icons do not sit flush against balances

Verification

DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer swift test --filter 'OpenRouter|DeepSeek|StatusItemAnimationTests|ProvidersPaneCoverageTests'

Note: git diff --check passes.