feat: releases from GitHub first, then git.kebcloud.no; releases sets others

Updates and install.sh try the GitHub mirror, then git.kebcloud.no,
each with a short timeout, and download from the first server with the
release, checked against its checksums.txt. The releases config option
(and LAZYSECRETS_RELEASES for install.sh) lists other servers. The
release workflow copies each release to GitHub when GH_RELEASE_TOKEN is
set. The status pane's issues link points to GitHub.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

README.md

@@ -37,8 +37,9 @@ On macOS or Linux (arm64 or x86_64):
 curl -fsSL https://git.kebcloud.no/keb/lazysecrets/raw/branch/main/install.sh | sh
 ```
 
-It installs the latest [release](https://git.kebcloud.no/keb/lazysecrets/releases)
-into `~/.local/bin` after checking it against the release's checksums.
+It installs the latest release, from GitHub or else
+[git.kebcloud.no](https://git.kebcloud.no/keb/lazysecrets/releases), into
+`~/.local/bin` after checking it against the release's checksums.
 `sh -s -- v0.2.0` installs a given version, `LAZYSECRETS_INSTALL_DIR`
 somewhere else.
 
@@ -96,8 +97,8 @@ lazysecrets never stores, caches or sends your secret values. It keeps the
 names and metadata of what you've loaded in a cache file readable only by
 you, to show it at once next time (`cache: false` turns it off). It talks
 only to the services you use it with, and collects no usage data. The one
-call of its own is a daily check for a new release on this server, which
-`updateCheck: false` turns off.
+call of its own is a daily check for a new release, on GitHub or else
+git.kebcloud.no, which `updateCheck: false` turns off.
 
 ## Repositories