Dolt merge engine: detect conflicts between player branch and main

[theinterneti]

Part of #270

Implement WorldReconciliationService.detect_conflicts(player_branch). Parse DOLT_MERGE conflicts to identify: which entities were modified by both player and other sources, what the diverging values are.

Acceptance Criteria

• WorldReconciliationService.detect_conflicts(player_branch) → List[ConflictRecord]
• Uses DOLT_MERGE --no-commit to detect without applying
• ConflictRecord: {table, row_id, player_value, main_value, entity_description}
• Handles all three conflict types: update/update, insert/insert, delete/update
• Unit tests with synthetic conflicting branches