test: add unit tests for ActionExecutor tool dispatch and payload passthrough (Issue #115)

[rafaio1]

Summary

Adds unit tests verifying ActionExecutor correctly dispatches to registered tools by name, passes payload and context through without modification, handles async tools, and throws on unregistered tool names.

Tests Added

• ✅ Dispatches to correct registered tool by name
• ✅ Payload passed through to tool execute without modification
• ✅ Context passed through to tool execute
• ✅ Throws TOOL_NOT_FOUND for unregistered tool names
• ✅ Returns async tool results correctly

Verification

All 5 tests pass locally via npx vitest run tests/actions/action-executor.test.ts.

Closes #115