docs(packaging): write INSTALL-GITHUB.md (wget + dpkg -i / rpm -i / apk add --allow-untrusted)

[satwareAG-ironMike]

Context

Documentation for users who want to download packages directly from GitHub Releases (without adding our APT/YUM/APK repo). This is the simplest install path: one wget, one dpkg -i / rpm -i / apk add.

Acceptance Criteria

• docs/packaging/INSTALL-GITHUB.md exists
• Covers: finding the right asset on the GitHub Releases page
• Shows Debian/Ubuntu: wget <url> && sudo dpkg -i *.deb
• Shows RHEL/Fedora: wget <url> && sudo rpm -i *.rpm
• Shows Alpine: wget <url> && sudo apk add --allow-untrusted *.apk
• Notes the limitation: no apt upgrade / dnf upgrade (manual update only)
• Links to INSTALL-DEBIAN.md for the repo-based approach (recommended)

Dependencies

• TIME type encoding/decoding broken in v7.0.0-rc.2 (OO API regression) #21 (GitHub Releases upload) — assets must be attached to releases

Suggested Test Plan

1. Follow the docs: download from GitHub Releases, install manually
2. Verify extension loads on each distro family