fix: meld builder validation for red fives and chi sequences

[rysb-dev]

Summary

Fixes two bugs in the meld builder UI:

Bug 1: Red Five Duplicate Selection

Previously, when using the pon/chi/kan meld builder, users could add more than one red five (aka dora) of the same suit (e.g., 0p, 0p, 0p). The fix:

• Include meld builder tiles in tileCounts so the palette updates in real-time as tiles are selected
• Properly check red five availability using the separate red5m/red5p/red5s count keys
• Update TilePalette to check both disabled tiles and proper counts for red fives

Bug 2: Invalid Chi Meld Sequences

Previously, the chi meld builder allowed any tiles of the same suit, even non-consecutive ones (e.g., 5p5p5p or 2m4m6m). Now:

• Added getChiAllowedTiles() function that computes valid tiles based on current selection
• First tile: any numbered (non-honor) tile
• Second tile: same suit, within ±2 of first tile, able to complete a sequence
• Third tile: only the tile that completes the 3-consecutive sequence
• Invalid tiles are visually grayed out and unclickable in the palette

Bonus: Pon/Kan Improvement

For pon/kan/ankan melds, after the first tile is selected, all other tile types are now disabled in the palette (previously only enforced in code, not visually).

Testing

• npm run check passes (only pre-existing a11y warnings)
• npm run build succeeds
• Manual testing recommended for the meld builder flows