Update documentation for multi-distro support

[mairas]

Description

Update documentation to reflect the new multi-distro structure.

Files to Update

• apt.hatlabs.fi/README.md - Add section on extended naming
• apt.hatlabs.fi/docs/SPEC.md - Update with component structure
• Component repo README files - Document suffix requirement

Documentation to Create

• Component repository template/guide for adding suffix
• Migration guide for future packages

Acceptance Criteria

• All documentation updated
• Component repo template created
• Migration guide written
• README files reference Issue Multi-distro package support with extended naming convention #28

Dependencies

• Update documentation for multi-distro support #40 (validation complete)

Implementation Requirements

MANDATORY: Follow halos-distro/docs/DEVELOPMENT_WORKFLOW.md during implementation.

Related to #28