Architectural: OR register slugs are org-wide unique, breaking cross-user template clones

[rubenvdlinde]

Problem

Surfaced while investigating #51. OpenBuilt's `ApplicationsController::provisionPerAppRegister` provisions the per-app register as `openbuilt-{slug}` regardless of caller. OR's register-slug uniqueness is organisation-wide. Net effect: when user B tries to clone a template that user A already cloned (same slug), the register-creation step hits the unique constraint and the API returns 500.

Per REQ-OBT-005 / templates-marketplace spec, different users SHOULD be able to clone the same template under their own ownership.

Options

1. Namespace register slugs by owner — `openbuilt-{owner}-{slug}`. Simplest, but uglier register names and surfaces UID in OR.
2. Use UUIDs for register names — `openbuilt-{uuid}`. Opaque but stable; deep-links to OpenRegister still work via API.
3. Auto-suffix on collision — `openbuilt-{slug}`, `openbuilt-{slug}-2`, ... Sluggable but loses determinism.

The versioned-app model (ADR-002) already uses `openbuilt-{slug}-{tier}` for per-version registers, which would inherit the same problem if two users cloned the same template.

Scope

• Update `provisionPerAppRegister` + `provisionPerVersionRegister` (wizard path) to use the chosen naming scheme.
• Catch + reformat the unique-constraint failure as a clean 409 with a meaningful error code, regardless of which option is chosen — never bubble a raw DB exception.
• Update `MigrateToVersionedModel` to handle the new naming convention.
• Update Newman + Postman collections to assert the new behaviour.

Filed as follow-up to #51 fix (PR #76).

[rubenvdlinde]

Fixed in #78 (merged) via owner-aware register-slug fallback: legacy openbuilt-{slug} reused when the existing register's owner matches the caller; openbuilt-{ownerUid}-{slug} when a different user already owns the legacy slug.