Fix heat loop list scrolling and ordering

[maddavo]

Summary

• Resize the loop-list ScrollRect content when more loops exist than fit in the viewport.
• Keep loop widgets ordered by numeric loop ID regardless of vessel-part discovery order.
• Add an unreleased changelog entry.

Verification

• dotnet build Source/SystemHeat.csproj --configuration Release --no-restore succeeds with 0 warnings and 0 errors.
• Tested in KSP with a four-loop vessel: all loops are reachable by scrolling and display in order 0, 1, 2, 3.

The branch is based directly on upstream master.