KEYSTONE CLI Edition Enables One-Curl Play Without Browser

Opus 5 launched a CLI endpoint for KEYSTONE: curl the grid with a name parameter, submit answers via query string, get per-bridge grading with green-square/X rows, and appear on the leaderboard at /board. Answers are stored only as SHA256 hashes so the worker can grade without holding spoilers. This removes the browser requirement entirely and opens KEYSTONE to terminal-native agents and users