Port Real Camera to Minecraft 1.21.11

[rsdadada]

Summary

• create the Minecraft 1.21.11 port directly from the current 26.1/dev implementation
• move the build and CI toolchain to Java 21 and the 1.21.11 Fabric/NeoForge dependency matrix
• restore Fabric's remapping pipeline with official Mojang mappings and update AW/AT metadata
• adapt GUI, picture-in-picture, camera, render-state, submit-node, feature-storage, key binding, and client message APIs to their 1.21.11 signatures
• preserve the 26.1 routing, model capture, camera roll, dynamic crosshair, raycast, configuration/UI, and compatibility behavior

Why

Minecraft 1.21.11 differs from 26.1 in its Java requirement, mapping/remapping model, loader build configuration, dependency versions, GUI lifecycle, camera entry points, and renderer submission APIs. This port keeps the current 26.1 source structure and implementation as the baseline and changes only the incompatible boundaries.

Version-specific differences

• Java 21 and Mixin JAVA_21
• Fabric Loom remap plugin with official Mojang mappings and a named source access widener
• GuiGraphics render lifecycle and 1.21.11 GUI/PIP state packages
• Camera.setup plus a GameRenderer.getFov invoker instead of the 26.1 camera hooks
• 1.21.11 SubmitNodeCollector, feature storage, block/item submission, and render-state signatures
• Fabric SpecialGuiElementRegistry / KeyBindingHelper and NeoForge 21.11 metadata/API ranges
• remap-safe access to RenderSetup.textures

Validation

• .\\gradlew.bat :common:clean :fabric:clean :fabric:build --no-daemon --max-workers=1 --console=plain --stacktrace
• .\\gradlew.bat :common:clean :neoforge:clean :neoforge:build --no-daemon --max-workers=1 --console=plain --stacktrace
• git diff --check
• verified Fabric production Mixin annotations and access widener are remapped to intermediary
• verified NeoForge Mixin targets and access transformer remain correct Mojmap/named descriptors
• independently audited all 17 registered Mixin/accessor targets against the 1.21.11 classes