fix(usage): support searchable API key filter on /usage page

[hansnow]

Summary

• keep the existing /usage API key filter UI as a Select, but make it searchable
• stop preloading only the first 100 API keys and load matching candidates on demand through the existing /keys API
• add regression coverage for the new Select search event and the user usage page filter flow

Problem

The user usage page could only filter API keys from a preloaded list, which made the control effectively unsearchable and also meant keys beyond the first 100 entries were hard to reach.

Solution

• add an optional search event to the shared Select component
• update the user usage page to debounce remote key lookup and keep the selected key label stable across result refreshes
• preserve existing usage query, stats, pagination, sorting, and CSV export behavior

Testing

• docker run --rm -v "$PWD/frontend:/app" -w /app node:24-alpine sh -lc 'corepack enable && corepack prepare pnpm@10.33.0 --activate && pnpm install --frozen-lockfile && pnpm exec vitest run src/components/common/__tests__/Select.spec.ts src/views/user/__tests__/UsageView.spec.ts && pnpm run typecheck'
• cd deploy && POSTGRES_PASSWORD=testpass JWT_SECRET=0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef TOTP_ENCRYPTION_KEY=abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789 ADMIN_PASSWORD=admin123 docker compose -f docker-compose.dev.yml build sub2api
• manual browser verification completed locally by the reporter

Demo

screen recording

sub2api-pr-1692-demo.mp4