fix: remove out-of-scope plan files and gofmt test file

Address review feedback on PR #13:
- Remove docs/superpowers/plans/ files not related to issue #4
- gofmt internal/mail/resolve_thread_test.go

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/mail/resolve_thread_test.go

@@ -83,4 +83,4 @@ func TestResolveThreadID_LookupError_ReturnsMessageID(t *testing.T) {
 	}
 }
 
-var nilLookup = func(string) (*database.Task, error) { return nil, nil }
+var nilLookup = func(string) (*database.Task, error) { return nil, nil }