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/db/db.go

@@ -0,0 +1,48 @@
+package db
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"time"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+func Connect(ctx context.Context, dsn string) (*pgxpool.Pool, error) {
+	cfg, err := pgxpool.ParseConfig(dsn)
+	if err != nil {
+		return nil, fmt.Errorf("parse dsn: %w", err)
+	}
+	cfg.MaxConns = 10
+	cfg.MinConns = 1
+	cfg.MaxConnLifetime = time.Hour
+	cfg.HealthCheckPeriod = time.Minute
+
+	var pool *pgxpool.Pool
+	var lastErr error
+	backoff := time.Second
+	for attempt := 1; attempt <= 10; attempt++ {
+		pool, err = pgxpool.NewWithConfig(ctx, cfg)
+		if err == nil {
+			pingCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
+			err = pool.Ping(pingCtx)
+			cancel()
+			if err == nil {
+				return pool, nil
+			}
+			pool.Close()
+		}
+		lastErr = err
+		slog.Warn("db connect attempt failed", "attempt", attempt, "error", err)
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		case <-time.After(backoff):
+		}
+		if backoff < 15*time.Second {
+			backoff *= 2
+		}
+	}
+	return nil, fmt.Errorf("connect to database after retries: %w", lastErr)
+}

backend/internal/db/migrate.go

@@ -0,0 +1,41 @@
+package db
+
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+
+	"database/sql"
+	"github.com/golang-migrate/migrate/v4"
+	"github.com/golang-migrate/migrate/v4/database/pgx/v5"
+	"github.com/golang-migrate/migrate/v4/source/iofs"
+	_ "github.com/jackc/pgx/v5/stdlib"
+)
+
+// Migrate applies all up migrations from the given fs (root contains *.sql files).
+func Migrate(dsn string, migrations fs.FS) error {
+	source, err := iofs.New(migrations, ".")
+	if err != nil {
+		return fmt.Errorf("migrations source: %w", err)
+	}
+
+	sqlDB, err := sql.Open("pgx", dsn)
+	if err != nil {
+		return fmt.Errorf("open sql db: %w", err)
+	}
+	defer sqlDB.Close()
+
+	driver, err := pgx.WithInstance(sqlDB, &pgx.Config{})
+	if err != nil {
+		return fmt.Errorf("migrate driver: %w", err)
+	}
+
+	m, err := migrate.NewWithInstance("iofs", source, "pgx", driver)
+	if err != nil {
+		return fmt.Errorf("migrate instance: %w", err)
+	}
+	if err := m.Up(); err != nil && !errors.Is(err, migrate.ErrNoChange) {
+		return fmt.Errorf("migrate up: %w", err)
+	}
+	return nil
+}