Define TypeScript Types

[prosdev]

📋 Spec: specs/phase-1-core-sdk/tasks.md#task-1

Implement TypeScript type definitions for the plugin system.

Files to create:

• packages/core/src/types/plugin.types.ts
• packages/core/src/types/sdk.types.ts
• packages/core/src/types/capability.types.ts
• packages/core/src/types/index.ts

Acceptance Criteria:

• All types export from index.ts
• TypeScript compiles with strict mode
• No any types in public APIs
• JSDoc comments on all exports

Depends on: None
Blocks: Tasks #2, #3, #4, #5, #6