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/photos/pipeline.go

@@ -0,0 +1,69 @@
+package photos
+
+import (
+	"bytes"
+	"image"
+	"time"
+
+	"github.com/disintegration/imaging"
+	"github.com/gen2brain/webp"
+	"github.com/rwcarlsen/goexif/exif"
+)
+
+type ImageMeta struct {
+	Width     int
+	Height    int
+	MimeType  string
+	TakenAt   *time.Time
+	Latitude  *float64
+	Longitude *float64
+	Thumb     []byte
+	Preview   []byte
+}
+
+func inspect(data []byte) (width, height int, ok bool) {
+	cfg, _, err := image.DecodeConfig(bytes.NewReader(data))
+	if err != nil {
+		return 0, 0, false
+	}
+	return cfg.Width, cfg.Height, true
+}
+
+func extractEXIF(data []byte) (taken *time.Time, lat, lon *float64) {
+	x, err := exif.Decode(bytes.NewReader(data))
+	if err != nil {
+		return nil, nil, nil
+	}
+	if dt, err := x.Get(exif.DateTimeOriginal); err == nil {
+		if s, err := dt.StringVal(); err == nil {
+			if t, err := time.Parse("2006:01:02 15:04:05", s); err == nil {
+				utc := t.UTC()
+				taken = &utc
+			}
+		}
+	}
+	if la, lo, err := x.LatLong(); err == nil {
+		lat, lon = &la, &lo
+	}
+	return taken, lat, lon
+}
+
+func buildVariants(data []byte) (thumb, preview []byte, err error) {
+	img, err := imaging.Decode(bytes.NewReader(data), imaging.AutoOrientation(true))
+	if err != nil {
+		return nil, nil, err
+	}
+	thumbImg := imaging.Fit(img, 200, 200, imaging.Lanczos)
+	previewImg := imaging.Fit(img, 1200, 1200, imaging.Lanczos)
+
+	opts := webp.Options{Quality: 82}
+	var thumbBuf bytes.Buffer
+	if err := webp.Encode(&thumbBuf, thumbImg, opts); err != nil {
+		return nil, nil, err
+	}
+	var previewBuf bytes.Buffer
+	if err := webp.Encode(&previewBuf, previewImg, opts); err != nil {
+		return nil, nil, err
+	}
+	return thumbBuf.Bytes(), previewBuf.Bytes(), nil
+}