Add "Entity Is Mapped to Salesforce" condition

Problem/Motivation

While checking if a mapping exists is useful, workflows also need to know if a specific entity has already been synced to Salesforce.

This enables:
- Different handling for new vs existing Salesforce records
- Checking sync status before operations
- Building workflows that depend on mapping state

Steps to reproduce

1. Create an ECA model
2. Need to check if specific entity is mapped to Salesforce
3. No condition to check mapped object existence

Proposed resolution

Add a condition that checks if a specific entity has a mapped object record in Salesforce.

Remaining tasks

- [ ] Create condition plugin
- [ ] Query mapped object storage
- [ ] Return TRUE/FALSE
- [ ] Provide tokens for Salesforce ID if mapped
- [ ] Test with mapped and unmapped entities

User interface changes

New condition "Entity is mapped to Salesforce" will appear in ECA.

API changes

None.

Data model changes

None.