refactor: implement _summary_list_field function to streamline handling of summary fields in coach summary; enhance payload processing and validation for string and list types

refactor: streamline evidence generation in coach summary; enhance JSON output contract and improve tokenization handling for local chat

refactor: add functions for JSON payload extraction and validation in coach summary; streamline summary key handling and improve error reporting

refactor: introduce compact representation functions for metrics, issues, and knowledge cards; enhance summary evidence generation and improve error handling in JSON extraction

refactor: enhance JSON response handling in coach summary generation; update response format instructions and improve error reporting for invalid JSON outputs

chore: add ninja-build and build-essential to package requirements; update README and documentation to reflect changes in model configuration and local Transformers usage

feat: expand coach summary training pipeline

feat: expand coach retrieval with equipment and goal overlays

test: cover external coach knowledge retrieval

feat(slm): add llama.cpp coach summary provider

feat(coach): add local transformers provider

Implement grounded coach summary with HF SLM