Enable log content lookup on API key usage page - #886

What changed

• make stored input/output token counts clickable on /manage/apikey-usage
• reuse the existing log content modal for formatted and raw content views
• fetch content through the existing public API-key-scoped endpoint
• close any open content modal when the active key is cleared

Why

The API key usage page already lists logs with stored content, and the backend already exposes a key-scoped content endpoint, but the page did not connect those existing pieces. Users therefore could not inspect their own request input/output from the page.

This keeps the existing backend authorization boundary: the presented API key must own the requested log. Management-only request details are not exposed.

Validation

• API key usage page tests: 3 passed
• lint, design token, import boundary, file size, dependency audit, production build, and bundle budget checks passed
• full test run: 1015 passed; one unrelated existing ConfigPage payload-rules test failed (this PR does not modify config code)