Add loading indicator when switching projects

[yandanp]

Description

When switching between projects, there's a brief moment where the workspace is empty. A loading indicator would improve the perceived performance.

Task

Add a subtle loading state (spinner or skeleton) when:

• Switching active project
• Loading terminal sessions
• Loading project workspace

Tech

• Frontend only (React/TypeScript)
• Workspace component: src/renderer/components/Workspace.tsx
• Use Tailwind CSS for styling (animate-pulse or animate-spin)

Getting Started

See CONTRIBUTING.md for setup instructions.