Add Architecture Guard to community catalog (#2430)

* feat: add Architecture Guard to community catalog

- Add architecture-guard v1.4.0 extension entry to catalog
- Add entry to README community extensions table
- Includes built-in Laravel-specific governance rules

* chore: update catalog timestamp to 2026-05-05

* fix: address PR feedback

- Add 'governance' category to README legend (used by Architecture Guard)
- Update architecture-guard timestamps to 2026-05-05 (submission date)
- Align with published extension behavior (Laravel support now built-in)

* chore: update Architecture Guard category to process

- Changed from 'governance' to 'process' (official category)
- Aligns with schema in EXTENSION-PUBLISHING-GUIDE.md
- Removed 'governance' from category legend (not an official category)

* chore: update timestamps to actual UTC datetime

- Top-level updated_at: 2026-05-05T07:26:00Z
- Entry created_at/updated_at: 2026-05-05T07:26:00Z
- Replaces placeholder 00:00:00Z with actual submission time