Closes#33
## Summary
- `_merge_helm_indexes` now parses each member's raw YAML first, then rewrites `urls` entries in-place via the new `_rewrite_urls` helper
- **Relative URLs** (e.g. `rancher-2.13.1.tgz`) are prepended with `{proxy_base}/api/v1/remote/{member_name}/`
- **Absolute URLs** matching `base_url` are rewritten to the proxy path (existing behaviour, now correct)
- **Absolute URLs** with a different prefix are left unchanged
- Removes the `_helm.resolve_content` raw-bytes detour from the virtual merge path; `remote/helm.py` is unchanged (still used for direct remote proxying)
## Test plan
- [x] 278 unit tests pass (`make test`)
- [x] New `TestRewriteUrls` class covering relative, absolute-match, absolute-no-match, leading-slash, and multi-URL cases
- [x] New `test_relative_urls_rewritten_to_proxy` in `TestMergeHelmIndexes`
- [x] Updated `test_first_member_wins_on_duplicate_name_and_version` to assert on proxy remote name (not upstream hostname)
- [x] Live Docker test: Rancher `index.yaml` relative URLs rewritten correctly to `http://localhost:8000/api/v1/remote/rancher-stable/rancher-2.14.1.tgz` etc.
- [x] `helm-all` virtual (19 members) returns HTTP 200 with 395k-line merged index on cache miss
Reviewed-on: #37
unkinben
624d858062