feat(web): add Stirling-PDF-style file preview, review panel, and tool chaining UX

After upload: dropzone replaced by image viewer with zoom controls.
After processing: review panel shows result preview, file info, download,
undo button, and suggested next tools for chaining.

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

@@ -10,6 +10,8 @@ interface FileState {
   error: string | null;
   originalSize: number | null;
   processedSize: number | null;
+  selectedFileName: string | null;
+  selectedFileSize: number | null;
   setFiles: (files: File[]) => void;
   setJobId: (id: string) => void;
   setProcessedUrl: (url: string | null) => void;
@@ -17,6 +19,8 @@ interface FileState {
   setProcessing: (v: boolean) => void;
   setError: (e: string | null) => void;
   setSizes: (original: number, processed: number) => void;
+  /** Clear processed result but keep the original uploaded file. */
+  undoProcessing: () => void;
   reset: () => void;
 }
 
@@ -29,13 +33,23 @@ export const useFileStore = create<FileState>((set, get) => ({
   error: null,
   originalSize: null,
   processedSize: null,
+  selectedFileName: null,
+  selectedFileSize: null,
   setFiles: (files) => {
     // Revoke old blob URL if any
     const old = get().originalBlobUrl;
     if (old) URL.revokeObjectURL(old);
     // Create a blob URL for the first file for before/after preview
     const blobUrl = files.length > 0 ? URL.createObjectURL(files[0]) : null;
-    set({ files, error: null, originalBlobUrl: blobUrl });
+    const firstName = files.length > 0 ? files[0].name : null;
+    const firstSize = files.length > 0 ? files[0].size : null;
+    set({
+      files,
+      error: null,
+      originalBlobUrl: blobUrl,
+      selectedFileName: firstName,
+      selectedFileSize: firstSize,
+    });
   },
   setJobId: (id) => set({ jobId: id }),
   setProcessedUrl: (url) => set({ processedUrl: url }),
@@ -44,6 +58,14 @@ export const useFileStore = create<FileState>((set, get) => ({
   setError: (e) => set({ error: e, processing: false }),
   setSizes: (original, processed) =>
     set({ originalSize: original, processedSize: processed }),
+  undoProcessing: () => {
+    set({
+      processedUrl: null,
+      jobId: null,
+      processedSize: null,
+      error: null,
+    });
+  },
   reset: () => {
     const old = get().originalBlobUrl;
     if (old) URL.revokeObjectURL(old);
@@ -56,6 +78,8 @@ export const useFileStore = create<FileState>((set, get) => ({
       error: null,
       originalSize: null,
       processedSize: null,
+      selectedFileName: null,
+      selectedFileSize: null,
     });
   },
 }));