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/auth/handlers.go

@@ -0,0 +1,93 @@
+package auth
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+
+	"shared-album/internal/httpx"
+)
+
+type Handler struct {
+	svc *Service
+}
+
+func NewHandler(svc *Service) *Handler { return &Handler{svc: svc} }
+
+type registerRequest struct {
+	Email    string `json:"email" binding:"required"`
+	Password string `json:"password" binding:"required"`
+	Name     string `json:"name" binding:"required"`
+}
+
+func (h *Handler) Register(c *gin.Context) {
+	var req registerRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		httpx.RespondError(c, httpx.BadRequest("invalid_request", "email, password and name are required"))
+		return
+	}
+	u, pair, err := h.svc.Register(c.Request.Context(), req.Email, req.Password, req.Name)
+	if err != nil {
+		httpx.RespondError(c, err)
+		return
+	}
+	c.JSON(http.StatusCreated, gin.H{"user": u.Public(), "tokens": pair})
+}
+
+type loginRequest struct {
+	Email    string `json:"email" binding:"required"`
+	Password string `json:"password" binding:"required"`
+}
+
+func (h *Handler) Login(c *gin.Context) {
+	var req loginRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		httpx.RespondError(c, httpx.BadRequest("invalid_request", "email and password are required"))
+		return
+	}
+	u, pair, err := h.svc.Login(c.Request.Context(), req.Email, req.Password)
+	if err != nil {
+		httpx.RespondError(c, err)
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{"user": u.Public(), "tokens": pair})
+}
+
+type refreshRequest struct {
+	RefreshToken string `json:"refresh_token" binding:"required"`
+}
+
+func (h *Handler) Refresh(c *gin.Context) {
+	var req refreshRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		httpx.RespondError(c, httpx.BadRequest("invalid_request", "refresh_token is required"))
+		return
+	}
+	pair, err := h.svc.Refresh(c.Request.Context(), req.RefreshToken)
+	if err != nil {
+		httpx.RespondError(c, err)
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{"tokens": pair})
+}
+
+func (h *Handler) Logout(c *gin.Context) {
+	var req refreshRequest
+	_ = c.ShouldBindJSON(&req)
+	if req.RefreshToken != "" {
+		if err := h.svc.Logout(c.Request.Context(), req.RefreshToken); err != nil {
+			httpx.RespondError(c, err)
+			return
+		}
+	}
+	c.Status(http.StatusNoContent)
+}
+
+func (h *Handler) Me(c *gin.Context) {
+	u, err := h.svc.store.GetUserByID(c.Request.Context(), UserID(c))
+	if err != nil {
+		httpx.RespondError(c, httpx.Unauthorized("unauthorized", "user not found"))
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{"user": u.Public()})
+}