Release: "latest" titled "Decoder <version>", moving tag, SHA256SUMS, Telegram on a version change #229

Goal

Bring the latest release in line with OpenIPC/vtesse, OpenIPC/vectis#39, OpenIPC/camex#60 and OpenIPC/cerberus#32. The policy of #194 stays: one release, latest, no releases per version, test pre-releases for reporters.

Current state (.github/workflows/build.yml:122-160)

• v2 uploads decoder-v2.apk and decoder-v2-mapping.txt, basic uploads decoder.apk, both into latest with softprops/action-gh-release (assets replaced).
• The latest tag never moves: it still points to 5c17905 (2025-09-02), so the release page shows that commit and the source archives are a year old.
• The title is latest, without the name or version, and the notes are empty.
• No SHA256SUMS.
• Every v2 and basic build is posted to Telegram.

Task

1. Title Decoder <version>: capital D, versionName of the v2 build (now Decoder 2.17). Short notes: the v2 version and commit, one line "decoder.apk: legacy basic ", a pointer to CHANGELOG.md (Add CHANGELOG.md with the version history #228) and the README.
2. Move the latest tag to the built v2 commit on every v2 publish, together with the title and notes. A basic build replaces only decoder.apk (and its line in the notes); it does not move the tag or change the title.
3. SHA256SUMS: after each upload, download the current release assets, recompute sha256sum over all of them (decoder-v2.apk, decoder-v2-mapping.txt, decoder.apk) and replace SHA256SUMS (--clobber). The two branches publish separately, so the file must cover both. Keep the concurrency rule (CI: concurrency, so an older run cannot overwrite the latest release #90) so two uploads do not race on it.
4. Telegram only when the version changes (decision of 2026-10-17, replaces "every build" of Releases: keep only latest and test pre-releases, no per-version releases #194): before replacing the asset, compare the new versionName with the one in the current release (the title for v2, the notes line for basic); post only a new version. Docs-only and CI-only pull requests no longer reach the channel.
5. basic stays in the release as the legacy app (decoder.apk).
6. Unchanged: decoder-v2-mapping.txt in the release (Reduce APK size: 107.5 KiB → ~104.5 KiB (already near the floor) #181), the test pre-releases (docs/testing.md:53).
7. Test pre-releases never take the place of latest, nor of each other: always --prerelease (never marked Latest, so releases/latest and its download links keep pointing at latest); a tag and an asset name of their own for every build (<device>-<issue>-test<N>, decoder-<device>-test<N>.apk), never decoder-v2.apk or decoder.apk; built by CI (the branch artifact), uploaded by hand; deleted when the test is over. Write this down in docs/testing.md:53.

Documentation (same PR)

• README.md, README.ru.md, README.zh-CN.md (one commit, same structure), section "Download":
  • permanent links: https://github.com/OpenIPC/decoder/releases/latest, https://github.com/OpenIPC/decoder/releases/latest/download/decoder-v2.apk, .../decoder.apk, .../SHA256SUMS;
  • the release title carries the v2 version; the history is in CHANGELOG.md;
  • Telegram gets each new version (not every build).
• docs/testing.md, "Versions and releases" (line 48 on): the title, the moving tag, SHA256SUMS, Telegram on a version change, CHANGELOG.md.
• Comments in build.yml (lines 11-14, 130-131).
• CHANGELOG.md: an entry for this change.

Order: #228 first. Related: #194, #181, #90, #230 (version MAJOR.MINOR.PATCH).