Implements SimulationManager.clone_simulation() and the corresponding
Flask route. The clone copies reddit_profiles.json, twitter_profiles.csv
and agent_profiles.json from the source simulation; does not copy
simulation_config.json; sets status=PROFILES_READY and records
parent_simulation_id. All 3 tests in test_simulation_clone.py pass.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>