feat(gui): redesign provider accounts workspace with adaptive grid, collapsible rails, and Cockpit Tools import

Summary of changes:
- Redesign provider accounts workspace with responsive two-column grid layout and container query adaptation for narrow screens.
- Introduce unified dropdown filter button with live counts for all accounts, Gemini/Claude active quotas, and exhausted states.
- Implement intuitive 4-option sorting (more/less headroom, soonest 5-hour and 7-day reset) with automatic active model context.
- Streamline quota windows to clean '5-Hour' and 'Weekly' metrics without repeating Gemini/Claude brand names or redundant percent badges.
- Provide clean unmasked email login by default with optional hidden (***) and alias display modes, and one-click clipboard copy.
- Add collapsible icon-only navigation sidebar (68px) and provider rail (58px) with smooth transitions and localStorage state persistence.
- Stabilize accounts overview stats card with 2x2 responsive grid under 960px container width and anchored refresh controls.
- Enhance account search bar with high-contrast surface background matching filter buttons and green focus glow.
- Replace native browser confirm with branded dark modal dialog for account deletion.
- Add AccountAuthChoiceModal for Google Antigravity providing clean choice between standard Google OAuth and Cockpit Tools token import.
- Support 1-click clipboard paste in Cockpit Tools with automatic JSON normalization and fallback to manual textarea.
- Include official Cockpit Tools AGCT asset and local encryption security guarantee footnote.
- Add comprehensive test suites in gui-account-quota-analysis.test.ts and provider-account-import.test.tsx with full 9-locale parity.

Author: agentHits