add file storage: metadata schema, minio upload/download, content-type extension mapping

- add files_metadata and files_metadata_connections tables with CRUD helpers
- add FileMetadata type and Sha256Hash typedef; replace Media struct
- add minio upload, presigned download URL, and key generation
- fix bucket existence check to use FileStorageBucketName instead of hardcoded "main"
- fix files_metadata_connections table name and trailing comma in DDL
- fix column name original -> name in files_metadata schema
- add canonical MIME-to-extension map with .unk fallback
- add FileDownloadLinkTtl constant (24h)

packages/postgresql/postgresql.go

@@ -67,6 +67,28 @@ func PgInit(ctx context.Context) {
 		panic(err)
 	}
 
+	_, err = dbConn.Exec(ctx, `
+		CREATE TABLE IF NOT EXISTS files_metadata (
+			id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+			uploader_id UUID NOT NULL REFERENCES users(id),
+			name TEXT,
+			hash TEXT NOT NULL,
+			created_at TIMESTAMP NOT NULL DEFAULT NOW()
+		)
+	`)
+	if err != nil {
+		panic(err)
+	}
+
+	_, err = dbConn.Exec(ctx, `
+		CREATE TABLE IF NOT EXISTS files_metadata_connections (
+			file_metadata_id UUID NOT NULL REFERENCES files_metadata(id) ON DELETE CASCADE,
+			connection_id UUID NOT NULL REFERENCES user_connections(id) ON DELETE CASCADE
+		)
+	`)
+	if err != nil {
+		panic(err)
+	}
 }
 
 func PgUserSave(ctx context.Context, user *types.User) error {
@@ -221,3 +243,57 @@ func PgConnectionGetMessagesBefore(ctx context.Context, before time.Time, connec
 	}
 	return messages, rows.Err()
 }
+
+func PgFileMetadataSave(ctx context.Context, metadata *types.FileMetadata) error {
+	_, err := dbConn.Exec(ctx, `
+		INSERT INTO files_metadata (id, uploader_id, name, hash, created_at) VALUES ($1, $2, $3, $4, $5)
+	`, metadata.Id, metadata.UploaderId, metadata.Name, metadata.Hash, metadata.CreatedAt)
+	return err
+}
+
+func PgFileMetadataGet(ctx context.Context, metadata *types.FileMetadata) error {
+	return dbConn.QueryRow(ctx, `
+		SELECT uploader_id, name, hash, created_at FROM files_metadata WHERE id = $1
+	`, metadata.Id).Scan(&metadata.UploaderId, &metadata.Name, &metadata.Hash, &metadata.CreatedAt)
+}
+
+func PgFileMetadataDelete(ctx context.Context, metadataId *uuid.UUID) error {
+	_, err := dbConn.Exec(ctx, `
+		DELETE FROM files_metadata WHERE id = $1 
+	`, metadataId)
+	return err
+}
+
+func PgFileConnectionsAdd(ctx context.Context, metadataId *uuid.UUID, connectionId *uuid.UUID) error {
+	_, err := dbConn.Exec(ctx, `
+		INSERT INTO files_metadata_connections (file_metadata_id, connection_id) VALUES ($1, $2)
+	`, metadataId, connectionId)
+	return err
+}
+
+func PgFileConnectionsGet(ctx context.Context, metadata *types.FileMetadata) error {
+	rows, err := dbConn.Query(ctx, `
+		SELECT connection_id FROM files_metadata_connections WHERE file_metadata_id = $1
+	`, metadata.Id)
+	if err != nil {
+		return err
+	}
+	defer rows.Close()
+
+	for rows.Next() {
+		connectionId := uuid.UUID{}
+		if err = rows.Scan(&connectionId); err != nil {
+			return err
+		}
+		metadata.Connections = append(metadata.Connections, connectionId)
+	}
+	return rows.Err()
+}
+
+func PgFileMetadataHashExists(ctx context.Context, hash *types.Sha256Hash) (bool, error) {
+	var exists bool
+	err := dbConn.QueryRow(ctx, `
+		SELECT EXISTS (SELECT FROM files_metadata WHERE hash = $1)
+	`, hash).Scan(&exists)
+	return exists, err
+}