feat: photo rename and viewer delete with confirmation

Backend:
- add PATCH /api/photos/:id to rename original_filename (uploader/owner/admin)
- emit photo.updated SSE event

Frontend:
- inline filename editor in the right panel
- viewer: back button (arrow_back) on the left, delete on the right
- delete confirmed via a modal dialog; filmstrip updates after deletion

backend/internal/photos/handlers.go

@@ -93,6 +93,24 @@ func (h *Handler) Get(c *gin.Context) {
 	c.JSON(http.StatusOK, gin.H{"photo": p})
 }
 
+type renameRequest struct {
+	OriginalFilename string `json:"original_filename" binding:"required"`
+}
+
+func (h *Handler) Rename(c *gin.Context) {
+	var req renameRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		httpx.RespondError(c, httpx.BadRequest("invalid_request", "original_filename is required"))
+		return
+	}
+	p, err := h.svc.Rename(c.Request.Context(), c.Param("id"), auth.UserID(c), req.OriginalFilename)
+	if err != nil {
+		httpx.RespondError(c, err)
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{"photo": p})
+}
+
 func (h *Handler) Download(c *gin.Context) {
 	url, err := h.svc.Download(c.Request.Context(), c.Param("id"), auth.UserID(c))
 	if err != nil {