[Monorepo] Delete template.json at the end of the compatibility bridge #1187

Summary

ADR 0029 (#1089) keeps templates/template.json on main for 90 days after the cg init retirement release, then deletes it. After deletion, cg init in already-installed CLIs fails with a download error; that behavior cannot be changed in packages users already have.

Deadline: release date of @common-grants/cli 0.5.0 + 90 days; fill in when the retirement release ships
Owner: named when the retirement release ships

On the recorded deadline, delete the manifest, its bridge-only integrity-check workflow and CODEOWNERS or ruleset entry, and remove the now-empty templates/ directory. Announce the removal alongside the retirement notice (release notes and docs).

Acceptance criteria

• Deadline date and owner are filled in above when the retirement release ships
• On the recorded deadline, delete templates/template.json and its bridge-only integrity check and review controls; templates/ no longer exists
• Verify the legacy raw GitHub manifest URL on main is unavailable after deletion
• The removal is announced where the retirement was announced
• No active workflow or configuration depends on the removed templates/ content, and current onboarding instructions do not direct readers to it; preserve historical references in ADRs and changelogs