feat: add progress bar to collage processing

Uses XMLHttpRequest upload progress to track image upload (0-80%),
then shows "Processing collage..." for the server-side compositing
phase (80-100%). Progress bar with percentage shown in the preview area.

apps/web/src/components/tools/collage-preview.tsx

@@ -61,12 +61,7 @@ export function CollagePreview() {
   }
 
   if (phase === "processing") {
-    return (
-      <div className="flex flex-col items-center justify-center h-full gap-3">
-        <Loader2 className="h-8 w-8 text-primary animate-spin" />
-        <p className="text-sm text-muted-foreground">Creating your collage...</p>
-      </div>
-    );
+    return <ProcessingView />;
   }
 
   if (phase === "result" && resultUrl) {
@@ -150,6 +145,29 @@ function UploadArea() {
   );
 }
 
+function ProcessingView() {
+  const progress = useCollageStore((s) => s.progress);
+  const label = progress < 80 ? "Uploading images..." : "Processing collage...";
+
+  return (
+    <div className="flex flex-col items-center justify-center h-full gap-4 px-8">
+      <Loader2 className="h-8 w-8 text-primary animate-spin" />
+      <div className="w-full max-w-xs space-y-2">
+        <div className="flex items-center justify-between text-sm text-muted-foreground">
+          <span>{label}</span>
+          <span className="font-mono">{progress}%</span>
+        </div>
+        <div className="h-2 w-full rounded-full bg-muted overflow-hidden">
+          <div
+            className="h-full rounded-full bg-primary transition-all duration-300 ease-out"
+            style={{ width: `${progress}%` }}
+          />
+        </div>
+      </div>
+    </div>
+  );
+}
+
 /** The live CSS Grid collage canvas. */
 function CollageCanvas({ template }: { template: CollageTemplate }) {
   const store = useCollageStore();

apps/web/src/components/tools/collage-settings.tsx

@@ -63,11 +63,11 @@ export function CollageSettings() {
     if (!hasImages || !template) return;
 
     store.setPhase("processing");
+    store.setProgress(0);
     store.setError(null);
 
     try {
       const formData = new FormData();
-      // Send images in cell-assignment order
       for (let i = 0; i < template.cells.length; i++) {
         const imgIdx = cellAssignments[i] ?? -1;
         if (imgIdx >= 0 && images[imgIdx]) {
@@ -94,18 +94,50 @@ export function CollageSettings() {
         }),
       );
 
-      const res = await fetch("/api/v1/tools/collage", {
-        method: "POST",
-        headers: formatHeaders(),
-        body: formData,
+      const result = await new Promise<{
+        downloadUrl: string;
+        processedSize: number;
+        originalSize: number;
+        jobId: string;
+      }>((resolve, reject) => {
+        const xhr = new XMLHttpRequest();
+        xhr.open("POST", "/api/v1/tools/collage");
+
+        const headers = formatHeaders();
+        headers.forEach((value, key) => {
+          xhr.setRequestHeader(key, value);
+        });
+
+        xhr.upload.onprogress = (e) => {
+          if (e.lengthComputable) {
+            store.setProgress(Math.round((e.loaded / e.total) * 80));
+          }
+        };
+
+        xhr.onload = () => {
+          if (xhr.status >= 200 && xhr.status < 300) {
+            store.setProgress(100);
+            try {
+              resolve(JSON.parse(xhr.responseText));
+            } catch {
+              reject(new Error("Invalid response"));
+            }
+          } else {
+            try {
+              const body = JSON.parse(xhr.responseText);
+              reject(new Error(body.error || `Failed: ${xhr.status}`));
+            } catch {
+              reject(new Error(`Failed: ${xhr.status}`));
+            }
+          }
+        };
+
+        xhr.onerror = () => reject(new Error("Network error"));
+        xhr.send(formData);
+
+        store.setProgress(5);
       });
 
-      if (!res.ok) {
-        const body = await res.json().catch(() => ({}));
-        throw new Error(body.error || `Failed: ${res.status}`);
-      }
-
-      const result = await res.json();
       store.setResult(result.downloadUrl, result.processedSize, result.originalSize, result.jobId);
     } catch (err) {
       store.setError(err instanceof Error ? err.message : "Collage failed");

apps/web/src/stores/collage-store.ts

@@ -50,6 +50,7 @@ interface CollageState {
   // UI state
   selectedCell: number | null;
   phase: Phase;
+  progress: number;
   resultUrl: string | null;
   resultSize: number | null;
   originalSize: number | null;
@@ -74,6 +75,7 @@ interface CollageState {
   setQuality: (v: number) => void;
   setSelectedCell: (v: number | null) => void;
   setPhase: (v: Phase) => void;
+  setProgress: (v: number) => void;
   setResult: (url: string, size: number, originalSize: number, jobId: string) => void;
   setError: (e: string | null) => void;
   reset: () => void;
@@ -105,6 +107,7 @@ export const useCollageStore = create<CollageState>((set, get) => ({
   quality: 90,
   selectedCell: null,
   phase: "upload",
+  progress: 0,
   resultUrl: null,
   resultSize: null,
   originalSize: null,
@@ -263,6 +266,7 @@ export const useCollageStore = create<CollageState>((set, get) => ({
   setQuality: (v) => set({ quality: v, resultUrl: null }),
   setSelectedCell: (v) => set({ selectedCell: v }),
   setPhase: (v) => set({ phase: v }),
+  setProgress: (v) => set({ progress: v }),
   setResult: (url, size, originalSize, jobId) =>
     set({ resultUrl: url, resultSize: size, originalSize, jobId, phase: "result", error: null }),
   setError: (e) => set({ error: e, phase: "editing" }),
@@ -287,6 +291,7 @@ export const useCollageStore = create<CollageState>((set, get) => ({
       quality: 90,
       selectedCell: null,
       phase: "upload",
+      progress: 0,
       resultUrl: null,
       resultSize: null,
       originalSize: null,