Improve joseki detection

[anoek]

No description provided.

[github-actions]

Code Review

I've reviewed this PR and found one potential bug:

Bug: Center intersection ignored in joseki detection

Location: src/engine/ai/categorize.ts:278-280 (in the new getZones function)

The new code returns an empty array when a move is placed at the exact center intersection on boards 13x13 or larger:

// Center intersection is ignored (no zones)
if (inVerticalBand && inHorizontalBand) {
    return [];
}

Issue: When getZones() returns an empty array, the move won't be tracked in any zone for joseki detection. The loop in detectJosekiMoves (line 411) will simply skip over it:

for (const zone of zones) {  // zones is empty [], so loop never executes
    if (!zoneState.still_joseki[zone]) {
        continue;
    }
    // ... joseki tracking logic
}

Impact: Center point moves (tengen) won't be counted toward joseki move limits or score loss thresholds in any zone. While tengen isn't common in traditional joseki, this could lead to unexpected behavior where center moves are silently excluded from analysis.

Suggestion: Consider whether center moves should belong to all 4 middle zones (4,5,6,7) instead of being excluded entirely, or document why center moves are intentionally ignored.