chore: bump version to v2026.4.312 and add changelog entry}
- Bump build version from v2026.4.311 to v2026.4.312 across all docs
- Bump package.json version from 2026.4.312 to 2026.4.313
- Add v2026.4.312 changelog entry for footer clear fix in layout
- Update version references in AGENTS.md, INSTALL.md, README.md,
change-break.md, todo.md, and artifacts docs