T11: Create LLMBased redactor with guard protection

[dpaluy]

Task Details

Priority: p2 | Story Points: 3 | Group: C (Integration)
Depends on: T1, T3

Files

• lib/tracebook/redactors/llm_based.rb
• test/lib/redactors/llm_based_test.rb

Acceptance Criteria

• IsolatedExecutionState guard prevents infinite recursion
• Provider abstraction for OpenAI, Anthropic, Ollama
• Sync and async modes work
• Configurable timeout and on_failure behavior
• Security warning documented for external providers

Context

Part of PII Redaction Architecture Refactor - Phase 3: LLM Redactor

See full plan: docs/plans/260106-02b-pii-redaction-architecture.md