feat: add multi-environment variable groups support

[kud1]

feat: add multi-environment variable groups support

Implement environment variable groups feature that allows users to
define and switch between different sets of environment variables
for different deployment contexts (dev, staging, production, etc.)

New features:

• EnvGroupSelector component for quick group switching in prompt bar
• Support for creating, editing, and deleting environment groups
• Active group selection persists across sessions
• Backward compatible with existing single env configuration

Changes:

• Add EnvGroupSelector.tsx component
• Add EnvGroup interface to api.ts
• Extend ClaudeSettings with envGroups and activeEnvGroup fields
• Add group management UI in Settings.tsx
• Integrate group selector in FloatingPromptInput.tsx

Also includes:

• Fix chat loading hang by using static imports for Tauri APIs
• Code style cleanup (quote normalization, trailing commas)