feat: implement shared-album multi-user photo album

Backend (Go/Gin/pgx): env config, pgx pool with retries, Garage S3 client
(path-style, region garage), embedded golang-migrate migrations, JWT auth with
refresh rotation, albums CRUD, members/roles/invites with no-escalation matrix,
photo upload + async imaging/goexif WebP variants, cursor pagination, presigned
URLs, likes/comments, SSE hub (album + personal), notifications, share links.

Frontend (SvelteKit 2 + Svelte 5 + Tailwind v4): API wrapper with 401 refresh,
auth store, all screens, Uploader/PhotoGrid/Lightbox/Comments, SSE client with
reconnect + REST catch-up, three themes + system via data-theme.

Deploy without Docker: Makefile builds the frontend into backend/static and
embeds it (go:embed) into a single statically linked binary; systemd unit and
nginx SSE example included.

Use gen2brain/webp (-tags nodynamic) instead of cgo kolesa-team/go-webp to keep
CGO_ENABLED=0 static builds; design.md/proposal.md updated accordingly.

backend/internal/albums/store.go

@@ -0,0 +1,100 @@
+package albums
+
+import (
+	"context"
+	"errors"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgxpool"
+
+	"shared-album/internal/httpx"
+	"shared-album/internal/models"
+)
+
+var ErrNotFound = errors.New("album not found")
+
+type Store struct {
+	pool *pgxpool.Pool
+}
+
+func NewStore(pool *pgxpool.Pool) *Store { return &Store{pool: pool} }
+
+func (s *Store) Create(ctx context.Context, a *models.Album) error {
+	return s.pool.QueryRow(ctx,
+		`INSERT INTO albums (id, owner_id, title, description, cover_photo_id)
+		 VALUES ($1, $2, $3, $4, $5)
+		 RETURNING created_at, updated_at`,
+		a.ID, a.OwnerID, a.Title, a.Description, a.CoverPhotoID,
+	).Scan(&a.CreatedAt, &a.UpdatedAt)
+}
+
+func (s *Store) OwnerID(ctx context.Context, id string) (string, error) {
+	var ownerID string
+	err := s.pool.QueryRow(ctx, `SELECT owner_id FROM albums WHERE id = $1`, id).Scan(&ownerID)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return "", httpx.NotFound("album_not_found", "album not found")
+		}
+		return "", err
+	}
+	return ownerID, nil
+}
+
+func (s *Store) GetByID(ctx context.Context, id string) (*models.Album, error) {
+	var a models.Album
+	err := s.pool.QueryRow(ctx,
+		`SELECT id, owner_id, title, description, cover_photo_id, created_at, updated_at
+		 FROM albums WHERE id = $1`, id).
+		Scan(&a.ID, &a.OwnerID, &a.Title, &a.Description, &a.CoverPhotoID, &a.CreatedAt, &a.UpdatedAt)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, ErrNotFound
+		}
+		return nil, err
+	}
+	return &a, nil
+}
+
+func (s *Store) ListForUser(ctx context.Context, userID string) ([]models.Album, error) {
+	rows, err := s.pool.Query(ctx,
+		`SELECT a.id, a.owner_id, a.title, a.description, a.cover_photo_id, a.created_at, a.updated_at
+		 FROM albums a
+		 LEFT JOIN album_members m ON m.album_id = a.id AND m.user_id = $1
+		 WHERE a.owner_id = $1 OR m.user_id IS NOT NULL
+		 ORDER BY a.created_at DESC`, userID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	out := []models.Album{}
+	for rows.Next() {
+		var a models.Album
+		if err := rows.Scan(&a.ID, &a.OwnerID, &a.Title, &a.Description, &a.CoverPhotoID, &a.CreatedAt, &a.UpdatedAt); err != nil {
+			return nil, err
+		}
+		out = append(out, a)
+	}
+	return out, rows.Err()
+}
+
+func (s *Store) Update(ctx context.Context, a *models.Album) error {
+	return s.pool.QueryRow(ctx,
+		`UPDATE albums
+		 SET title = $2, description = $3, cover_photo_id = $4, updated_at = now()
+		 WHERE id = $1
+		 RETURNING updated_at`,
+		a.ID, a.Title, a.Description, a.CoverPhotoID,
+	).Scan(&a.UpdatedAt)
+}
+
+func (s *Store) Delete(ctx context.Context, id string) error {
+	tag, err := s.pool.Exec(ctx, `DELETE FROM albums WHERE id = $1`, id)
+	if err != nil {
+		return err
+	}
+	if tag.RowsAffected() == 0 {
+		return ErrNotFound
+	}
+	return nil
+}