feat(ui): direct-download links for downloadable local repo files (#106)

## Why

The local-repo object browser renders every file name as inert text, so there is no way to grab a file from the UI even though local rpm repos already serve their contents as real yum repos. Users have to hand-construct URLs. This adds one-click downloads, built as a modular per-repo-type capability so other types can be switched on later with a single map entry.

## Changes

- Adds a `downloadableTypes` capability map (`ui/src/components/downloads.ts`) keyed by `package_type`; each entry builds the direct-download URL for a file.
- Enables `rpm`, pointing at the yum files route `/api/v2/remotes/<repo>/files/<path>` (path-segment-encoded).
- Renders file names in the object browser as `<a href download>` links when the repo's type is downloadable, and as plain text otherwise.
- Fetches the repo's `package_type` on the Objects page as the modularity hook and threads it through the tree rows.

## Notes

Download links are same-origin unauthenticated GETs (the API serves local repos with no token on reads, matching how yum clients fetch), so a bare `href` carries no credentials. Adding a future type is one entry in `downloadableTypes`.

---------

Co-authored-by: Ben Vin <neotheo@gmail.com>
Reviewed-on: #106
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

ui/src/components/downloads.ts

@@ -0,0 +1,36 @@
+// Per-repo-type "downloadable" capability map.
+//
+// When a repo's package_type has an entry here, file entries in the object
+// browser render as direct-download links pointing at the URL the entry
+// builds. Types absent from the map render as plain text. Enabling a new
+// type is a one-line addition below.
+//
+// Download routes are same-origin, unauthenticated GETs (the API serves local
+// repos as real registries with no token on reads), so a bare <a href download>
+// works and carries no credentials.
+
+// buildUrl receives the repo name and the artifact's full path (may contain
+// slashes) and returns the direct-download URL for that file.
+type DownloadUrlBuilder = (repo: string, path: string) => string;
+
+export const downloadableTypes: Record<string, DownloadUrlBuilder> = {
+  // rpm locals are real yum repos; files are served at
+  // /api/v2/remotes/<repo>/files/<path>.
+  rpm: (repo, path) =>
+    `/api/v2/remotes/${encodeURIComponent(repo)}/files/${path
+      .split('/')
+      .map(encodeURIComponent)
+      .join('/')}`,
+};
+
+// downloadUrlFor returns the direct-download URL for a file when its repo type
+// is downloadable, or null otherwise (render as plain text).
+export function downloadUrlFor(
+  packageType: string | undefined,
+  repo: string,
+  path: string,
+): string | null {
+  if (!packageType) return null;
+  const build = downloadableTypes[packageType];
+  return build ? build(repo, path) : null;
+}