Stable v2.6.1

• Revert "stable: promote v2.6.5"
• feat(sites): PHP memory_limit selectable up to 8G for legacy-app debugging
• fix(cra): US spelling (artifact) in SBOM handler — misspell gate
• feat(cra): SBOM export (CycloneDX 1.5) — the CRA Annex I Part II artefact
• docs(plan): correct channel/changelog description to the final design
• fix(changelog): public + stable changelog stop at the current stable version
• feat(dashboard): show the active update channel + mark testing versions
• fix(changelog): restore the granular per-release changelog for everyone
• feat(firewall): warn that GeoIP filters also block incoming email