chore: add clippy.toml, issue/PR templates, Helm OCI docs, logging env vars

- clippy.toml: cognitive-complexity=25, too-many-arguments=7
- Issue templates: bug report + feature request (YAML forms)
- PR template with checklist (fmt, clippy, test, unwrap, changelog)
- README: Helm OCI support documented, NORA_LOG_LEVEL/FORMAT env vars
- GitHub topic: helm-registry re-added (verified helm push/pull works)

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,16 @@
+## Summary
+
+<!-- What does this PR do? -->
+
+## Changes
+
+<!-- List key changes -->
+
+## Checklist
+
+- [ ]  passes
+- [ ]  passes
+- [ ]  passes
+- [ ] No  in production code
+- [ ] New public API has documentation
+- [ ] CHANGELOG updated (if user-facing change)