ci(release): split canary/stable tracks + unified Gitea Releases

A push to main publishes canary builds to canary channels (fast iteration,
unchanged); a single vX.Y.Z tag releases every platform at one version to the
stable channels and attaches all artifacts (.deb/.rpm/.msix/.apk/.aab/.dmg +
flatpak/decky/host-installer) to one Gitea Release. Collapses the
host-v*/win-v*/host-win-v* tag namespaces into v* — the channel split makes the
version-shadow bug structurally impossible (canary and stable are separate repos,
never a shared version line).

- scripts/ci/gitea-release.{sh,ps1}: one idempotent release helper
  (create-or-fetch + delete-before-upload), replacing 3 copy-pasted inline blocks
  and fixing their latent 409-on-reupload bug; prerelease flag auto-derived from
  the tag (an -rc tag won't shadow "Latest")
- channels: apt canary/stable distributions; rpm *-canary/base groups; flatpak
  canary/stable OSTree branches + a 2nd .Canary.flatpakref; generic-registry
  canary/ vs latest/ aliases; Play internal/alpha; Apple TestFlight vs notarized DMG
- android versionName threaded through gradle (versionCode stays run_number);
  Apple canary = TestFlight-only (no DMG/tvOS); canary base bumped to 0.3.0
- docs: new docs-site channels.md (subscribe table + cut-a-release runbook +
  box migration), refreshed ci.md workflow table + packaging READMEs

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packaging/windows/README.md

@@ -83,6 +83,8 @@ pwsh -File packaging\windows\pack-host-installer.ps1 -Version 0.0.0-dev -TargetD
 
 ## Release
 
-Push a `host-win-vX.Y.Z` tag — the workflow builds, signs, and publishes
-`punktfunk-host-setup-X.Y.Z.exe` + the public `.cer`, and refreshes the `latest/` alias. Main pushes
-publish rolling `0.2.<run>` builds (no `latest/` update).
+Push a `vX.Y.Z` tag — one tag releases every platform (see
+[Release Channels](https://punktfunk.unom.io/docs/channels)). The workflow builds, signs, and
+publishes `punktfunk-host-setup-X.Y.Z.exe` + the public `.cer`, refreshes the stable `latest/`
+alias, and attaches the installer to the unified Gitea Release. Main pushes publish rolling
+`0.3.<run>` **canary** builds to the `canary/` alias.