Add linux-aurora: Apple Silicon kernel for the edge and rc channels

Aurora Silicon's fork of the Asahi kernel (DisplayPort alt-mode and USB4
for external displays, VRR, ISP and AOP drivers) as an aarch64-only split
package, linux-aurora and linux-aurora-headers, pinned to an immutable
commit that was cold-boot qualified on a MacBook Pro 14" M1 Pro and 16"
M2 Max. It provides and conflicts with linux-asahi so Macs move over in
one explicit transaction, and pkgrel 9 orders it after the last build the
maralcbr fork published, so already-installed Macs upgrade on -Syu.

Metadata: skip_build like the x86 kernels (built only by its own PR),
release_ring fast with channels edge and rc, so one merge publishes the
same artifact to edge/aarch64 and rc/aarch64 and stable keeps asahi-alarm's
linux-asahi. No x86 job is emitted and no shared tooling changes.

pkgbuilds/linux-aurora/.omarchy/package.json

@@ -0,0 +1,6 @@
+{
+  "source": "local",
+  "skip_build": true,
+  "release_ring": "fast",
+  "channels": ["edge", "rc"]
+}