fix: address SPEC-21 code quality issues

refactor: implement proper middleware architecture (SPEC-21)

refactor(orchestrator): Introduce WorkflowState dataclass (Priority 7) (#129)

refactor(factory): Implement Provider Registry Pattern (Priority 6) (#128)

refactor(config): Remove dead config and Anthropic references (Priority 4)

fix(huggingface): P1 Free Tier tool execution - Remove premature marker (#121)

fix(P1): Replace stale 72B model fallbacks with 7B to avoid Novita 500 errors

fix(P0): Auto-detect OpenAI provider from BYOK api_key prefix

fix: Address CodeRabbit review feedback

fix(P0): Complete HuggingFace tool calling integration and document framework display bug

fix(P0): Add function invoking marker and improve ChatMessage extraction

fix(P0): Complete bi-directional tool support for HuggingFace (sync+streaming)

fix(P0): Implement proper AIFunction serialization for HuggingFace

fix(P1): Resolve HuggingFace 401 - invalid token was root cause

fix(auth): Robust HF_TOKEN loading and debug logging for Partner API auth failure

fix(P1): Switch from Llama-3.1-70B to Qwen2.5-72B for HuggingFace free tier

feat(SPEC-16): Unified Chat Client Architecture (#115)