test(tools): add unit tests for error handling functions

* Implement tests for error functions like errRequiredField, errInvalidField, and errEntityNotFound.
* Ensure proper metadata is returned for various error scenarios.
* Validate error handling in CRM, Files, and other tools.
* Introduce tests for parsing stored file IDs and UUIDs.
* Enhance coverage for helper functions related to project resolution and session management.

internal/tools/links.go

@@ -62,7 +62,7 @@ func (t *LinksTool) Link(ctx context.Context, _ *mcp.CallToolRequest, in LinkInp
 	}
 	relation := strings.TrimSpace(in.Relation)
 	if relation == "" {
-		return nil, LinkOutput{}, errInvalidInput("relation is required")
+		return nil, LinkOutput{}, errRequiredField("relation")
 	}
 	if _, err := t.store.GetThought(ctx, fromID); err != nil {
 		return nil, LinkOutput{}, err