Automatically detect board size from SGF SZ property

[Samtroulcode]

Summary

Automatically set KataGo's boardXSize and boardYSize from the SGF root
SZ property.

This allows 9x9, 13x13, 19x19, and rectangular boards to be analyzed without
manually overriding the board dimensions for each file.

Behavior

• SZ[9] sets a 9x9 board
• SZ[13] sets a 13x13 board
• SZ[19] sets a 19x19 board
• SZ[13:9] sets a 13x9 rectangular board
• Missing or invalid SZ values preserve the configured board dimensions
• Explicit command-line board-size overrides remain supported

Changes

• Parse square and rectangular SGF board sizes
• Apply detected dimensions to KataGo analysis queries
• Use the detected board height when formatting variations
• Add unit tests for valid, invalid, missing, and rectangular sizes
• Document automatic board-size detection

Tests

• npm test
• npm run lint