Telegram: post the binaries of a new version as files, no text announcement #40

Goal

The OpenIPC Telegram dev channel gets build files only, for the archive and test downloads — no text announcements, no CHANGELOG excerpts (decision of 2026-10-17; the text post of OpenIPC/vectis 1.9.0 (the same step is here since #38) was not wanted). OpenIPC/vtesse, OpenIPC/decoder and OpenIPC/camex already post their APKs as files.

Task

• Replace the sendMessage text post with the release binaries sent as files: one post with sendMediaGroup (documents: the four cerberus-<arch>), a short caption on the last one — Cerberus <version> for Linux, commit, time, the releases/latest link, nothing from CHANGELOG.md.
• Only for a new version, as now; missing secrets or a failed upload are a warning, not a failed release.
• READMEs (all three): replace "every new version is announced in the Telegram channels" with "the binaries of every new version are also posted to the OpenIPC Telegram channel".
• Workflow and docs only: no version bump.