fix(shiny): pass image_path to SNIC renderer and add default sample image

The rendered_svg() reactive was calling render_puzzle_svg() without
image_path, so uploaded images never displayed. Now passes
pos$parameters$image_path through to the renderer.

Also ships a default sample image (purple asters, 400x600, 146KB)
so SNIC puzzles work out of the box without requiring an upload.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: pjt222

inst/extdata/sample_image.jpg

@@ -0,0 +1,24 @@
+# Resize a source photo to a small default sample image for SNIC puzzle demos
+# Run once: Rscript inst/scripts/generate_default_image.R
+#
+# Source: PJT_6805.jpg (purple asters, Norway 2017)
+# Photo by Philipp Thoss
+
+if (!requireNamespace("magick", quietly = TRUE)) {
+  stop("magick package required: install.packages('magick')")
+}
+
+source_path <- commandArgs(trailingOnly = TRUE)[1]
+if (is.na(source_path) || !file.exists(source_path)) {
+  stop("Usage: Rscript inst/scripts/generate_default_image.R <path-to-source-image>")
+}
+output_path <- file.path("inst", "extdata", "sample_image.jpg")
+
+img <- magick::image_read(source_path)
+img <- magick::image_resize(img, "400x")
+magick::image_write(img, output_path, format = "jpeg", quality = 85)
+
+cat("Default image saved to:", output_path, "\n")
+cat("Dimensions:", paste(magick::image_info(img)$width, "x",
+    magick::image_info(img)$height), "\n")
+cat("File size:", file.size(output_path), "bytes\n")

inst/scripts/generate_default_image.R

@@ -1272,8 +1272,13 @@ build_puzzle_params <- function(input, puzzle_type = NULL) {
   has_fusion <- !is.null(fusion_groups_str) && nchar(trimws(fusion_groups_str)) > 0
 
   # SNIC-specific
-  image_path_val <- if (puzzle_type == "snic" && !is.null(input$snic_image)) {
-    input$snic_image$datapath
+  image_path_val <- if (puzzle_type == "snic") {
+    if (!is.null(input$snic_image)) {
+      input$snic_image$datapath
+    } else {
+      # Fall back to bundled sample image
+      system.file("extdata", "sample_image.jpg", package = "jigsawR")
+    }
   } else {
     NULL
   }
@@ -1850,7 +1855,7 @@ server <- function(input, output, session) {
       "concentric" = "Ring-based puzzle radiating from center",
       "voronoi" = "Organic irregular shapes from Voronoi tessellation",
       "random" = "Random Delaunay triangulation shapes",
-      "snic" = "Image-aware superpixel segmentation (requires image)",
+      "snic" = "Image-aware superpixel segmentation (upload your own or use sample)",
       ""
     )
     tags$small(class = "text-muted", desc)
@@ -1927,7 +1932,8 @@ server <- function(input, output, session) {
         show_labels = show_labels_value,
         label_color = label_color_value,
         label_size = label_size_value,
-        inline = TRUE  # Omit XML declaration for inline HTML embedding
+        inline = TRUE,  # Omit XML declaration for inline HTML embedding
+        image_path = pos$parameters$image_path
       )
       result
     }, error = function(e) {