Fix build_config_from_refinement to handle both list and data frame returns from ellmer

Merge pull request #2 from awellis/feature/implementation

Switch license from MIT to GPL-3 (matches loo/brms ecosystem)

Add end-to-end examples for skill proposer and structure optimizer

Fix devtools::check() issues: escape Rd link, add NSE globals, fix compute_loo chain_id

Update gitignore for R package artifacts

Add structure optimizer: iteration loop, LLM refinement, JSONL logging, patience stopping

Refactor skill proposer for package: roxygen docs, no library() calls, returns loading_structure

Add LLM reflection module with structured output for model refinement

Add model comparison, problem flagging, and LLM reflection prompt formatting

Add model fitting with cmdstanr, diagnostics extraction, and LOO-CV

Add identifiability pre-check and SBC wrapper

Add data simulation engine with per-block theta generation and SBC generator

Add compilation matrix test: all 64 block combinations compile

Add Stan data preparation and model compilation with content-hash caching