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

internal/database/rpm_metadata.go

@@ -33,29 +33,29 @@ func (db *DB) InsertRPMMetadata(ctx context.Context, meta *provider.RPMMetadata)
 }
 
 type RPMMetadataRow struct {
-	RepoName    string
-	FilePath    string
-	ContentHash string
-	Name        string
-	Epoch       int
-	Version     string
-	Release     string
-	Arch        string
-	Summary     string
-	Description string
-	RPMSize     int64
+	RepoName      string
+	FilePath      string
+	ContentHash   string
+	Name          string
+	Epoch         int
+	Version       string
+	Release       string
+	Arch          string
+	Summary       string
+	Description   string
+	RPMSize       int64
 	InstalledSize int64
-	License     string
-	Vendor      string
-	Group       string
-	BuildHost   string
-	SourceRPM   string
-	URL         string
-	Packager    string
-	Requires    json.RawMessage
-	Provides    json.RawMessage
-	Files       json.RawMessage
-	Changelogs  json.RawMessage
+	License       string
+	Vendor        string
+	Group         string
+	BuildHost     string
+	SourceRPM     string
+	URL           string
+	Packager      string
+	Requires      json.RawMessage
+	Provides      json.RawMessage
+	Files         json.RawMessage
+	Changelogs    json.RawMessage
 }
 
 func (db *DB) ListRPMMetadataEntries(ctx context.Context, repoName string) ([]provider.RPMMetadata, error) {