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

@@ -0,0 +1,129 @@
+package database
+
+import (
+	"context"
+	"encoding/json"
+
+	"git.unkin.net/unkin/artifactapi/internal/provider"
+)
+
+func (db *DB) InsertRPMMetadata(ctx context.Context, meta *provider.RPMMetadata) error {
+	requiresJSON, _ := json.Marshal(meta.Requires)
+	providesJSON, _ := json.Marshal(meta.Provides)
+	filesJSON, _ := json.Marshal(meta.Files)
+	changelogsJSON, _ := json.Marshal(meta.Changelogs)
+
+	_, err := db.Pool.Exec(ctx, `
+		INSERT INTO rpm_metadata (
+			repo_name, file_path, content_hash,
+			name, epoch, version, release, arch,
+			summary, description, rpm_size, installed_size,
+			license, vendor, build_group, build_host, source_rpm, url, packager,
+			requires, provides, files, changelogs
+		) VALUES ($1,$2,$3,$4,$5,$6,$7,$8,$9,$10,$11,$12,$13,$14,$15,$16,$17,$18,$19,$20,$21,$22,$23)
+		ON CONFLICT (repo_name, file_path) DO NOTHING
+	`,
+		meta.RepoName, meta.FilePath, meta.ContentHash,
+		meta.Name, meta.Epoch, meta.Version, meta.Release, meta.Arch,
+		meta.Summary, meta.Description, meta.RPMSize, meta.InstalledSize,
+		meta.License, meta.Vendor, meta.Group, meta.BuildHost, meta.SourceRPM, meta.URL, meta.Packager,
+		requiresJSON, providesJSON, filesJSON, changelogsJSON,
+	)
+	return err
+}
+
+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
+	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
+}
+
+func (db *DB) ListRPMMetadataEntries(ctx context.Context, repoName string) ([]provider.RPMMetadata, error) {
+	rows, err := db.ListRPMMetadata(ctx, repoName)
+	if err != nil {
+		return nil, err
+	}
+	result := make([]provider.RPMMetadata, len(rows))
+	for i, r := range rows {
+		meta := provider.RPMMetadata{
+			RepoName:      r.RepoName,
+			FilePath:      r.FilePath,
+			ContentHash:   r.ContentHash,
+			Name:          r.Name,
+			Epoch:         r.Epoch,
+			Version:       r.Version,
+			Release:       r.Release,
+			Arch:          r.Arch,
+			Summary:       r.Summary,
+			Description:   r.Description,
+			RPMSize:       r.RPMSize,
+			InstalledSize: r.InstalledSize,
+			License:       r.License,
+			Vendor:        r.Vendor,
+			Group:         r.Group,
+			BuildHost:     r.BuildHost,
+			SourceRPM:     r.SourceRPM,
+			URL:           r.URL,
+			Packager:      r.Packager,
+		}
+		json.Unmarshal(r.Requires, &meta.Requires)
+		json.Unmarshal(r.Provides, &meta.Provides)
+		json.Unmarshal(r.Files, &meta.Files)
+		json.Unmarshal(r.Changelogs, &meta.Changelogs)
+		result[i] = meta
+	}
+	return result, nil
+}
+
+func (db *DB) ListRPMMetadata(ctx context.Context, repoName string) ([]RPMMetadataRow, error) {
+	rows, err := db.Pool.Query(ctx, `
+		SELECT repo_name, file_path, content_hash,
+			name, epoch, version, release, arch,
+			summary, description, rpm_size, installed_size,
+			license, vendor, build_group, build_host, source_rpm, url, packager,
+			requires, provides, files, changelogs
+		FROM rpm_metadata
+		WHERE repo_name = $1
+		ORDER BY name, epoch, version, release, arch
+	`, repoName)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var result []RPMMetadataRow
+	for rows.Next() {
+		var r RPMMetadataRow
+		if err := rows.Scan(
+			&r.RepoName, &r.FilePath, &r.ContentHash,
+			&r.Name, &r.Epoch, &r.Version, &r.Release, &r.Arch,
+			&r.Summary, &r.Description, &r.RPMSize, &r.InstalledSize,
+			&r.License, &r.Vendor, &r.Group, &r.BuildHost, &r.SourceRPM, &r.URL, &r.Packager,
+			&r.Requires, &r.Provides, &r.Files, &r.Changelogs,
+		); err != nil {
+			return nil, err
+		}
+		result = append(result, r)
+	}
+	return result, rows.Err()
+}