Add image upload preview functionality; update titles and templates for consistency

Co-authored-by: Copilot <copilot@github.com>

frontend/app/static/app.js

@@ -18,6 +18,28 @@ document.addEventListener("DOMContentLoaded", () => {
     });
   }
 
+  // ── Image upload preview ───────────────────────────────
+  const imageInput = document.getElementById("reference_image");
+  const imagePreviewWrap = document.getElementById("image-upload-preview");
+  const imagePreview = document.getElementById("image-upload-preview-img");
+  const imageFilename = document.getElementById("image-upload-filename");
+
+  if (imageInput && imagePreviewWrap && imagePreview && imageFilename) {
+    imageInput.addEventListener("change", () => {
+      const file = imageInput.files && imageInput.files[0];
+      if (!file) {
+        imagePreviewWrap.hidden = true;
+        imagePreview.removeAttribute("src");
+        imageFilename.textContent = "";
+        return;
+      }
+
+      imagePreview.src = URL.createObjectURL(file);
+      imageFilename.textContent = file.name;
+      imagePreviewWrap.hidden = false;
+    });
+  }
+
   // ── Generate dropdown tabs ─────────────────────────────
   document.querySelectorAll(".tab-btn").forEach((btn) => {
     btn.addEventListener("click", () => {