Linux builds missing from update manifest (updates.openlogi.org) — in-app updater can never detect updates on Linux

**OpenLogi version**
0.8.3

**Operating system**
Linux (Ubuntu, installed via .deb from GitHub Releases)

**Description**
`check_for_updates` / `auto_install_updates` are enabled by default, but the app never finds updates on Linux. Root cause: the updater queries `https://updates.openlogi.org/channels/stable/latest.json` for update checks.

Fetching that manifest directly shows it only lists `"macos"` and `"windows"` asset entries — no `"linux"` entry at all — even though the matching GitHub Release (v0.8.3) does publish a linux .deb (`openlogi-v0.8.3-linux-amd64.deb`).

So the in-app updater can never detect or install updates on Linux, regardless of local config, because the release pipeline apparently doesn't push Linux build metadata into the update channel manifest, only to GitHub Releases.

**Steps to reproduce**
1. Install OpenLogi via the Linux .deb
2. Leave `check_for_updates`/`auto_install_updates` on (default)
3. Fetch `updates.openlogi.org/channels/stable/latest.json` and compare its asset list to the GitHub Releases page for the same version

**Expected**
Linux builds included in the update manifest so the built-in updater actually works on Linux.

Start by comparing the stable latest.json manifest with the matching GitHub Release and trace the release pipeline that publishes the update channel metadata. Check how check_for_updates and auto_install_updates consume the asset list. Done means the Linux .deb appears in the manifest and an installed Linux app can detect and install a newer release.

Written by the indexing model from the issue text.