ARM gains stable and rc channels with matching release safeguards

emirb merged omacom/omarchy#16065 into quattro, adding stable and rc package configurations for aarch64. Previously, even an rc ARM install would move to edge on its first update. Existing edge installations stay there until their owners choose another channel. Apple Silicon remains edge-only because its package sources support that channel alone. This is development-branch support, not evidence that Omarchy 4.5.0 stable has shipped.

ryanrhughes proposed and emirb merged omacom/omarchy-iso#298, allowing ARM release images to publish beside x86_64 images without replacing their download filename. The committed ISO builder change omacom/omarchy-iso@c6de4cc756bb also selects the matching ARM mirror for stable, rc or edge.

Package tooling changes on master align ARM builds with those channel snapshots and block stable promotion until its ARM mirror matches rc. These commits are attributed to Emir Beganovic. Separate commits attributed to Ryan Hughes remove package channel restrictions that had excluded NVIDIA components from ARM rc promotion, and prevent publication from replacing a channel's packages with equal or older versions. The safeguards are recorded in omacom/omarchy-pkgs@82fb44ba2e38, omacom/omarchy-pkgs@61ff00812591 and omacom/omarchy-pkgs@48340e7e3f0b.