Remove state mutations from scope_validator out-of-scope path

Fix final 3 state mutations: escalation, scope_validator, sanitizer now return partial dicts

Fix interview-critical issues: state mutation anti-pattern, documentation accuracy, prior frustration handling, security notes

Fix critical bugs: compensation for late orders, escalation detection, conversation history improvements

Fix 5 critical bugs: replace LLM scope validator with embedding similarity, add missing state fields, fix routing, improve timeout handling

Add scope validation and system capabilities: Handle meta queries and reject out-of-scope questions