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/social/handlers.go

@@ -0,0 +1,67 @@
+package social
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+
+	"shared-album/internal/auth"
+	"shared-album/internal/httpx"
+)
+
+type Handler struct {
+	svc *Service
+}
+
+func NewHandler(svc *Service) *Handler { return &Handler{svc: svc} }
+
+func (h *Handler) AddLike(c *gin.Context) {
+	if err := h.svc.AddLike(c.Request.Context(), c.Param("id"), auth.UserID(c)); err != nil {
+		httpx.RespondError(c, err)
+		return
+	}
+	c.Status(http.StatusNoContent)
+}
+
+func (h *Handler) RemoveLike(c *gin.Context) {
+	if err := h.svc.RemoveLike(c.Request.Context(), c.Param("id"), auth.UserID(c)); err != nil {
+		httpx.RespondError(c, err)
+		return
+	}
+	c.Status(http.StatusNoContent)
+}
+
+func (h *Handler) ListComments(c *gin.Context) {
+	list, err := h.svc.ListComments(c.Request.Context(), c.Param("id"), auth.UserID(c))
+	if err != nil {
+		httpx.RespondError(c, err)
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{"comments": list})
+}
+
+type commentRequest struct {
+	Text string `json:"text" binding:"required"`
+}
+
+func (h *Handler) AddComment(c *gin.Context) {
+	var req commentRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		httpx.RespondError(c, httpx.BadRequest("invalid_request", "text is required"))
+		return
+	}
+	comment, err := h.svc.AddComment(c.Request.Context(), c.Param("id"), auth.UserID(c), req.Text)
+	if err != nil {
+		httpx.RespondError(c, err)
+		return
+	}
+	c.JSON(http.StatusCreated, gin.H{"comment": comment})
+}
+
+func (h *Handler) DeleteComment(c *gin.Context) {
+	if err := h.svc.DeleteComment(c.Request.Context(), c.Param("id"), auth.UserID(c)); err != nil {
+		httpx.RespondError(c, err)
+		return
+	}
+	c.Status(http.StatusNoContent)
+}