Add deterministic stale and archive checks to the template registry

[OthmaneBlial]

Context

The v1 registry distinguishes verified, reference, and archived entries, but the state transition rules are only documented. A contributor should be able to prove that a stale entry stops satisfying the five-workflow verification gate without deleting its history.

Affected area

• scripts/validate_template_registry.mjs
• scripts/validate_template_registry.test.mjs
• docs/community-templates.md
• site showcase badges

Acceptance criteria

• Add fixtures covering verified -> reference and reference -> archived transitions.
• A reference or archived entry cannot satisfy a required verified workflow.
• An archived entry remains traceable in the catalog but is not rendered as currently verified.
• Validation errors name the manifest and failed state rule.
• The public template guide documents when each transition is appropriate.

Test command

node --test scripts/validate_template_registry.test.mjs
node scripts/validate_template_registry.mjs
npm --prefix site test -- tests/site.spec.mjs

Non-goals

• Automatically deleting stale templates.
• Contacting authors or opening issues automatically.
• Changing the immutable manifest schema URL.