Describe the bug

In main.go:3562, cache migration error is silently ignored:

_ = config.MigrateCacheFiles()

If migration fails, user runs with stale/missing cache data. No warning, no diagnostic.

To reproduce

1. Upgrade matcha with incompatible cache format
2. Migration fails silently
3. Previously cached data lost

Expected behavior

Log warning when migration fails so users can report issues.