ci: align nightly assets with version releases (#2699)

Publish GUI installers and Android APKs under their original names.
Use the built commit version in Core, Web and Magisk ZIP names, and
match the version-release archive layout while preserving executables.

Generate SHA256SUMS for all downloads and validate the packaged asset
manifest before publication. Cover native installers, archive layout,
checksums and invalid artifacts in the CI script tests.

Document versioned download URLs and remove the stable-URL claim.

.github/CI.md

@@ -53,6 +53,13 @@ events still handle full main builds dispatched manually by a maintainer.
 Nightly Release can also be started manually to publish existing main HEAD
 builds without rebuilding them.
 
+Nightly uses the same asset names and archive layout as version releases.
+Core, Web, and Magisk ZIP names include the built commit's version (for example,
+`easytier-linux-x86_64-v2.7.0.zip`). GUI installers and Android APKs retain their
+original filenames without an extra ZIP wrapper. `SHA256SUMS` covers every
+download. Asset URLs can change when the project version changes; use the
+fixed `nightly` release page to find the current files.
+
 ## Manual builds and releases
 
 Repository Write access is required. In Actions, run Core, GUI, and Mobile