Add Alpine/apk local repository support

The alpine provider hosted only remote (proxy) repos; there was no way to
publish first-party .apk packages the way rpm-local and deb-local already
allow. This extends the existing alpine provider into a real apk repository:
uploaded .apk files are parsed in pure Go and a per-arch APKINDEX.tar.gz is
generated on demand, at parity with rpm repodata and deb Packages generation.

- Implement LocalUploader/LocalIndexer/PostUploadHook/PostDeleteHook on the
  alpine provider, keeping the remote proxy methods intact.
- Parse .apk (concatenated gzipped tar streams) in pure Go: read .PKGINFO from
  the control stream and compute the apk pull checksum C: = Q1+base64(sha1) over
  the raw control gzip stream (not the whole file).
- Generate an unsigned per-arch APKINDEX.tar.gz (clients use --allow-untrusted),
  applying the same dot-segment normalization as deb for ./<arch>/... requests.
- Add AlpineMetadata plus separate Alpine store/reader/deleter interfaces so the
  rpm/deb metadata interfaces are not widened.
- Add the alpine_metadata table and its Insert/Delete/List DB methods.
- Add testsupport.MinimalApk plus unit tests (parse, Q1 checksum, per-arch
  filtering, dot-segment handling, validate) and a dockere2e index test.

internal/database/alpine_metadata.go

@@ -0,0 +1,70 @@
+package database
+
+import (
+	"context"
+	"strings"
+
+	"git.unkin.net/unkin/artifactapi/internal/provider"
+)
+
+func (db *DB) InsertAlpineMetadata(ctx context.Context, meta *provider.AlpineMetadata) error {
+	_, err := db.Pool.Exec(ctx, `
+		INSERT INTO alpine_metadata (
+			repo_name, file_path, content_hash, checksum,
+			name, version, arch, download_size, installed_size,
+			description, url, license, origin, maintainer,
+			build_time, commit_hash, provider_priority,
+			depends, provides, install_if
+		) VALUES ($1,$2,$3,$4,$5,$6,$7,$8,$9,$10,$11,$12,$13,$14,$15,$16,$17,$18,$19,$20)
+		ON CONFLICT (repo_name, file_path) DO NOTHING
+	`,
+		meta.RepoName, meta.FilePath, meta.ContentHash, meta.Checksum,
+		meta.Name, meta.Version, meta.Arch, meta.DownloadSize, meta.InstalledSize,
+		meta.Description, meta.URL, meta.License, meta.Origin, meta.Maintainer,
+		meta.BuildTime, meta.Commit, meta.ProviderPriority,
+		strings.Join(meta.Depends, " "), strings.Join(meta.Provides, " "), strings.Join(meta.InstallIf, " "),
+	)
+	return err
+}
+
+func (db *DB) DeleteAlpineMetadata(ctx context.Context, repoName, filePath string) error {
+	_, err := db.Pool.Exec(ctx, `DELETE FROM alpine_metadata WHERE repo_name = $1 AND file_path = $2`, repoName, filePath)
+	return err
+}
+
+func (db *DB) ListAlpineMetadataEntries(ctx context.Context, repoName string) ([]provider.AlpineMetadata, error) {
+	rows, err := db.Pool.Query(ctx, `
+		SELECT repo_name, file_path, content_hash, checksum,
+			name, version, arch, download_size, installed_size,
+			description, url, license, origin, maintainer,
+			build_time, commit_hash, provider_priority,
+			depends, provides, install_if
+		FROM alpine_metadata
+		WHERE repo_name = $1
+		ORDER BY name, version, arch
+	`, repoName)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var result []provider.AlpineMetadata
+	for rows.Next() {
+		var m provider.AlpineMetadata
+		var depends, provides, installIf string
+		if err := rows.Scan(
+			&m.RepoName, &m.FilePath, &m.ContentHash, &m.Checksum,
+			&m.Name, &m.Version, &m.Arch, &m.DownloadSize, &m.InstalledSize,
+			&m.Description, &m.URL, &m.License, &m.Origin, &m.Maintainer,
+			&m.BuildTime, &m.Commit, &m.ProviderPriority,
+			&depends, &provides, &installIf,
+		); err != nil {
+			return nil, err
+		}
+		m.Depends = strings.Fields(depends)
+		m.Provides = strings.Fields(provides)
+		m.InstallIf = strings.Fields(installIf)
+		result = append(result, m)
+	}
+	return result, rows.Err()
+}

internal/database/postgres.go

@@ -182,6 +182,35 @@ func (db *DB) migrate() error {
 
 		CREATE INDEX IF NOT EXISTS idx_deb_metadata_repo ON deb_metadata(repo_name);
 
+		CREATE TABLE IF NOT EXISTS alpine_metadata (
+			id                BIGSERIAL PRIMARY KEY,
+			repo_name         TEXT NOT NULL,
+			file_path         TEXT NOT NULL,
+			content_hash      TEXT NOT NULL,
+			checksum          TEXT NOT NULL,
+			name              TEXT NOT NULL,
+			version           TEXT NOT NULL,
+			arch              TEXT NOT NULL,
+			download_size     BIGINT DEFAULT 0,
+			installed_size    BIGINT DEFAULT 0,
+			description       TEXT DEFAULT '',
+			url               TEXT DEFAULT '',
+			license           TEXT DEFAULT '',
+			origin            TEXT DEFAULT '',
+			maintainer        TEXT DEFAULT '',
+			build_time        BIGINT DEFAULT 0,
+			commit_hash       TEXT DEFAULT '',
+			provider_priority TEXT DEFAULT '',
+			depends           TEXT DEFAULT '',
+			provides          TEXT DEFAULT '',
+			install_if        TEXT DEFAULT '',
+			created_at        TIMESTAMPTZ DEFAULT NOW(),
+			UNIQUE(repo_name, file_path)
+		);
+
+		CREATE INDEX IF NOT EXISTS idx_alpine_metadata_repo ON alpine_metadata(repo_name);
+		CREATE INDEX IF NOT EXISTS idx_alpine_metadata_repo_arch ON alpine_metadata(repo_name, arch);
+
 		CREATE TABLE IF NOT EXISTS github_rpm_sync_state (
 			remote_name        TEXT PRIMARY KEY,
 			etag               TEXT DEFAULT '',