Stable v2.6.2

• feat(release): stable release rebuilds current code at the stable version
• feat(cron): optional e-mail notification per cron job (none/errors/always)
• fix(agent): correct PowerDNS repo key + self-heal changed vendor keys
• feat(agent): add PowerDNS, MariaDB, Dovecot to vendor upstream repos
• feat(agent): pin package families to vendor current-stable repos (rspamd pilot)
• feat(cra): evidence snapshots — audit trail of CRA readiness over time
• feat(cra): incident register (Art. 14 reporting evidence)
• fix(deps): bump golang.org/x/text to v0.39.0 (GO-2026-5970)
• fix(release): stable promotion advances sequentially, not to testing tip