Port Amber to 26.2-rc-1

[iamkaf]

Ports Amber to the Minecraft 26.2 RC line.

This adds the 26.2-rc-1 Stonecutter version, updates the active version metadata, and adapts the Fabric block-outline hook for the 26.2 client renderer path.

Checked:

• Built Amber for 26.2-rc-1 during the port.
• Boot-checked the client to catch mixin startup failures.
• Used the local Amber artifact for downstream TeaKit, Amber Conformance, Konfig, and Liteminer validation.