Correct MRP feed support: drop GitHub Releases, note toggle and fallback

GitHub feeds don't implement publish-date ordering, so remove them from
the supported list. Add a note that feeds without publish dates (Maven,
GitHub) silently fall back to version ordering, and that the strategy is
gated behind the non-semver-ordering feature toggle.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: NickJosevski

src/pages/docs/releases/channels/index.md

@@ -120,6 +120,10 @@ By default, channels rank package versions using [Semantic Versioning (SemVer 2.
 
 #### Ordering strategy {#version-ordering-strategy}
 
+:::div{.hint}
+The **Use most recently published** ordering strategy is currently behind the `non-semver-ordering` feature toggle. While the toggle is disabled, the ordering strategy choice is unavailable and channels rank package versions using SemVer.
+:::
+
 Channels rank candidate package versions to decide which is the "latest" that satisfies the rule. Two strategies are available:
 
 - **Use semantic version** (default): packages are ranked by their version string using SemVer comparison. Use this when your package versions follow SemVer (e.g. `2.1.0`, `2.1.0-beta.3`). The version range and pre-release tag fields described above apply.
@@ -146,7 +150,9 @@ When **Use most recently published** is selected:
 The **Design rule** dialog isn't available for Most recently published rules — there's no SemVer range to evaluate candidates against. The regex filter determines which candidates qualify; Octopus then picks the candidate with the latest publish date. When two candidates share the same publish timestamp (a rare tie), the SemVer-higher version wins as a deterministic secondary sort.
 
 :::div{.hint}
-**Feed support.** Most recently published ordering needs the feed to report a publish date per version. It is supported on the built-in NuGet feed, external HTTP and filesystem NuGet feeds, Amazon S3, Google Cloud Storage, Helm, NPM, GitHub Releases, PyPI, and Artifactory Generic feeds. It is **not** supported on container or OCI registry feeds (Docker, DockerHub, GitHub Container Registry, Amazon ECR, Google GCR, or any OCI registry) because their tag-listing APIs return tag names only — fetching per-tag dates would require an extra manifest call for every tag. The channel rule editor warns you if you choose Most recently published with a step that targets one of these feeds.
+**Feed support.** Most recently published ordering needs the feed to report a publish date per version. It is supported on the built-in NuGet feed, external HTTP and filesystem NuGet feeds, Amazon S3, Google Cloud Storage, Helm, NPM, PyPI, and Artifactory Generic feeds. It is **not** supported on container or OCI registry feeds (Docker, DockerHub, GitHub Container Registry, Amazon ECR, Google GCR, or any OCI registry) because their tag-listing APIs return tag names only — fetching per-tag dates would require an extra manifest call for every tag. When you choose Most recently published for a step that targets one of these feeds, the channel rule editor warns you.
+
+Other feeds that don't report a publish date — including Maven and GitHub feeds — don't error, but they can't order by publish date either: they silently fall back to version-string ordering. Only use Most recently published with the feed types listed above.
 :::
 
 ### Git protection rules {#git-protection-rules}