Migrate development add-on builds away from legacy builder action

[sairon]

.github/workflows/builder.yml:121 still uses home-assistant/builder@2026.02.1 for the development add-on matrix build.

Migrate this workflow to the composite builder actions from home-assistant/builder#273 while preserving changed-add-on detection, current registry auth flow, and the add-on build behavior.

Done when:

• .github/workflows/builder.yml no longer references home-assistant/builder@
• PR/test and push/release builds still work for the add-on matrix
• the generic multi-arch image/manifests expected by the epic are published