Summary

• Delete 6 stale duplicate prompt files from root prompts/chat/ — backend resources/prompts/chat/ is the canonical source
• Update PathConstants.PROMPTS_DIR to point to autobot-backend/resources/prompts/ instead of root prompts/
• Update populate_knowledge_base.py glob paths to reference backend prompts
• Update 2 doc files referencing the old path

Closes #2472

Test plan

• No runtime code referenced root prompts/chat/ — only path_constants.py (now updated)
• Backend prompt_manager.py loads from resources/prompts/ (unchanged)
• Pre-commit hooks pass (black, isort, flake8, bandit)