fix: declare provider requirement in the artifactapi module

pre-commit runs `tofu validate`/tflint on modules/artifactapi standalone, where
no required_providers was declared, so OpenTofu inferred hashicorp/artifactapi
and failed (and tflint flagged missing required_version/version constraint).

- add modules/artifactapi/versions.tf declaring required_version and the
  artifactapi provider (source = the registry, version >= 0.1.2)
- drop the now-duplicate required_providers from root.hcl's generated backend.tf;
  keep the provider config block + backend. Declaring it in both the module and
  the generated root would be a "Duplicate required providers" error at runtime.

Also revert the earlier init lock-cleanup: the CI failure was stale provider
references in state (fixed with `tofu state replace-provider`), not the lock.

Makefile

@@ -16,11 +16,6 @@ define vault_env
 endef
 
 init:
-	@# Drop any stale dependency locks so provider sources are re-resolved
-	@# purely from config. Locks are gitignored and CI can reuse a workspace
-	@# carrying a lock from an earlier (old provider source) run, which -upgrade
-	@# on some OpenTofu versions tries to re-resolve instead of dropping.
-	@find . -name '.terraform.lock.hcl' -not -path '*/.git/*' -delete
 	@$(call vault_env) && \
 	terragrunt run --all --non-interactive init -- -upgrade