feat(photos): full EXIF metadata extraction, backfill and info panel

- backend: switch EXIF parser to dsoprea/go-exif/v3 (all recognised tags, numeric normalization); store in photos.exif jsonb (migration 000003); add storage.Get and cmd/backfill-exif to backfill existing photos from S3 originals
- frontend: info panel renders all EXIF attributes with RU labels, enum translation and units (1/N, f/N, mm, EV); service tags hidden
- viewer: remove make-cover action (cover managed from panel only), icon-only download
- openspec: sync lightroom-workspace-ui artifacts (EXIF, cover-from-panel) and add plan for configurable info attributes/labels stored in user profile

backend/cmd/backfill-exif/main.go

@@ -0,0 +1,75 @@
+package main
+
+import (
+	"bufio"
+	"context"
+	"log/slog"
+	"os"
+	"strings"
+
+	"shared-album/internal/config"
+	"shared-album/internal/db"
+	"shared-album/internal/photos"
+	"shared-album/internal/storage"
+)
+
+func main() {
+	loadDotEnv(".env")
+	loadDotEnv("../.env")
+
+	logger := slog.New(slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{Level: slog.LevelInfo}))
+	slog.SetDefault(logger)
+
+	cfg, err := config.Load()
+	if err != nil {
+		slog.Error("config error", "error", err)
+		os.Exit(1)
+	}
+
+	ctx := context.Background()
+
+	pool, err := db.Connect(ctx, cfg.Postgres.DSN())
+	if err != nil {
+		slog.Error("database connect failed", "error", err)
+		os.Exit(1)
+	}
+	defer pool.Close()
+
+	store, err := storage.New(ctx, cfg.S3)
+	if err != nil {
+		slog.Error("storage init failed", "error", err)
+		os.Exit(1)
+	}
+
+	photoStore := photos.NewStore(pool)
+	updated, err := photoStore.BackfillEXIF(ctx, store.Get)
+	if err != nil {
+		slog.Error("backfill failed", "error", err)
+		os.Exit(1)
+	}
+	slog.Info("exif backfill complete", "updated", updated)
+}
+
+func loadDotEnv(path string) {
+	f, err := os.Open(path)
+	if err != nil {
+		return
+	}
+	defer f.Close()
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		if line == "" || strings.HasPrefix(line, "#") {
+			continue
+		}
+		key, value, ok := strings.Cut(line, "=")
+		if !ok {
+			continue
+		}
+		key = strings.TrimSpace(key)
+		value = strings.TrimSpace(value)
+		if _, exists := os.LookupEnv(key); !exists {
+			_ = os.Setenv(key, value)
+		}
+	}
+}