feat: Add date-based ADR numbering format

[sgbett]

Summary

Support for configurable ADR numbering format has been added to the create-adr skill. Projects can now choose between sequential and date-based naming.

Configuration

In .architecture/config.yml:

adr:
  numbering_format: date-based  # or 'sequential' (default)

Formats

Format	Example Filename
sequential	ADR-001-use-react-for-frontend.md
date-based	20260125-ADR-use-react-for-frontend.md

Implementation

• Documented in .claude/skills/create-adr/SKILL.md
• Skill reads config to determine format before generating filename
• Sequential format scans existing ADRs for next number
• Date-based format uses current date (YYYYMMDD)

Related

• Commit: d96291d - docs: add configurable ADR numbering format to create-adr skill
• Default changed to date-based in commit 37ef4bd