any word graph, chosen by config name

[andy-k]

Summary

the endgame CLI used to pick its word graph from a small hardcoded table that mapped a lexicon name to a .kwg path, so solving a position with any word list outside that table meant recompiling the binary. this splits the two concerns apart: the argument now names only the alphabet, board layout, and tile set (english, catalan, dutch, french, german, norwegian, polish, slovene, spanish, or swedish) and never a specific word list, while a new argument takes a path to any .kwg built for that config and loads it straight from disk. the accompanying lab/endgame.txt documentation is updated to describe choosing any word graph by config name.

Changes

• now selects only the alphabet, board layout, and tile set; a new argument loads any .kwg from disk
• game_config_for_name replaces the old lexicon table for the CLI path
• solve_question and the CLI now delegate to a shared solve_position(game_config, kwg, ...), a pure extraction of the word-prune-and-solve logic
• score-diff moves to the 5th argument, following the config/kwg-file/fen/rack/score-diff order and hyphenated naming, with a usage line spelling out its sign (ahead, negative if behind)
• update lab/endgame.txt to document choosing any word graph by config name

Correctness

solve_question (the hardcoded demo's own path) is unchanged and still reads its own two lexicon kwg files by name; extracting solve_position carries no behavior change.