InvSort

Button placement is now coordinated through shared right-side slots.

• InvSort and InvSearch reserve ordered right-side inventory slots instead of using separate hard-coded heights.
• InvSearch now moves up into the first inventory button slot when InvSort is not installed.
• The shared Core exposes the occupied right-side button slots so companion mods can choose a free slot without overlapping Inventory Mods buttons.
• The slot API now reports available slot counts, remaining slot counts, and whether a requested or next slot fits before another mod places its button.
• Minecraft 26.x now uses one 26.1-26.2-pre-3 compatibility jar instead of separate 26.1.x and 26.2 pre-release build entries.