rust:1.88-slim has an empty package cache. apt-get install git
was failing with 'Unable to locate package git'.
Add apt-get update -qq before every apt-get install in checkout steps.
Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>
actions/checkout@v4 requires Node.js which is not in rust:1.88-slim.
Replace with direct git init+fetch+checkout using the Gitea instance URL.
Also fix release.yml: each build job creates the release (idempotent)
and uploads its own artifacts inline via Gitea API.
Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>