feat: add local RPM repository with on-demand repodata

Upload RPMs to local repos. Metadata is parsed async after upload
using cavaliergopher/rpm and stored in rpm_metadata table. Repodata
(repomd.xml, primary.xml.gz, filelists.xml.gz, other.xml.gz) is
generated on-demand from the DB — nothing stored in S3.

- RPM provider implements LocalUploader (validates .rpm extension,
  stores under Packages/)
- RPM provider implements PostUploadHook (async goroutine parses RPM
  headers, extracts name/version/arch/deps/etc into rpm_metadata)
- RPM provider implements LocalIndexer (serves repodata/* paths by
  querying rpm_metadata and generating XML on the fly)
- New provider interfaces: PostUploadHook, BlobReader, MetadataStore,
  RPMMetadataReader
- New rpm_metadata table with JSONB columns for requires/provides/
  files/changelogs

Tested e2e: upload cowsay RPM → repodata generated → dnf install
from local repo

go.sum

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 github.com/bsm/gomega v1.27.10/go.mod h1:JyEr/xRbxbtgWNi8tIEVPUYZ5Dzef52k01W3YH0H+O0=
+github.com/cavaliergopher/rpm v1.3.0 h1:UHX46sasX8MesUXXQ+UbkFLUX4eUWTlEcX8jcnRBIgI=
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 github.com/cenkalti/backoff/v4 v4.3.0/go.mod h1:Y3VNntkOUPxTVeUxJ/G5vcM//AlwfmyYozVcomhLiZE=
 github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=