Add integration tests for run command

[mgoldsborough]

Summary

The run command has unit tests for utility functions (parsePackageSpec, getCacheDir, resolveArgs), but lacks integration tests for the main handleRun function and error handling paths.

Current Test Coverage

• parsePackageSpec - parsing @scope/name@version specs
• getCacheDir - cache directory path generation
• resolveArgs - ${__dirname} placeholder resolution

Proposed Tests

Test	Value	Effort	Notes
Integration: handleRun with mock bundle	High	Medium	Mock registry client, verify spawn args
--update flag forces re-download	Medium	Medium	Verify cache is invalidated
PYTHONPATH env var set correctly	Medium	Low	Verify deps/ is prepended
Error handling: missing manifest	Medium	Medium	Should throw clear error
Error handling: network errors	Medium	Medium	Graceful failure with message

Implementation Notes

• Consider using vitest mocking for RegistryClient and spawn
• Could create a test fixture .mcpb bundle for integration tests
• Python PYTHONPATH test could verify env object without spawning

Files

• src/commands/packages/run.ts - implementation
• src/commands/packages/run.test.ts - existing unit tests