Remove deleted catalog locations from the demo configuration #128

Part of #85.

The local starter config and production config register missing examples/entities.yaml, examples/org.yaml and examples/acme-corp.yaml. The first two files were removed in #115 when examples/all.yaml became the source for the sample catalogue. A fresh demo therefore attempts to ingest missing locations.

Remove the obsolete file locations from both configs and add a regression test that resolves every configured file location from packages/backend and verifies it is a readable, non-empty file. Retain the local default catalogue and aggregate examples location, which includes the Acme sample entities. This is a config and test slice with no layout change.

Acceptance criteria

• Neither config references any of the three missing files.
• Every top-level file location in both configs exists and is readable.
• Both configs still load examples/all.yaml for guest users, groups and templates.
• mise run install, mise run lint and mise run test pass; attempt mise run build and record any environment blocker.