feat(client): improve workspace tab navigation

[Dustella]

Summary

• add position-aware gradient blur affordances when workspace tabs overflow
• increase tab height, spacing, typography, icon size, and close-button target
• include currently open tabs in Ctrl+K search with localized status badges and direct tab switching
• avoid duplicate repository results when the matching repository tab is already open

Validation

• pnpm --filter @oh-my-github/client test -- src/renderer/i18n/locales.test.ts
• pnpm typecheck
• pnpm --filter @oh-my-github/client build

Closes #11