Show inline image previews for binary files

Add inline image preview support for binary image files in diffs and the file viewer. Frontend: new CSS rules for diff/viewer image panels and macOS window radius, JS templates to render base64 image previews and wire previewMime/previewBase64 into rendering flow, plus applyPlatformChrome to set platform-specific chrome. Backend (Tauri): add base64 and ico deps and expose image preview data (mime + base64) on GitFileDiff and LocalRepoFile; implement mime detection, size-limited preview generation (5MB), .ico → PNG extraction, and integration into get_file_diff and local_repo_file to return previews when available. Also updates icon asset.

frontend/js/app.js

@@ -130,6 +130,10 @@ function currentPlatform() {
   return "linux";
 }
 
+function applyPlatformChrome() {
+  appRoot.dataset.platform = currentPlatform();
+}
+
 function currentTauriWindow() {
   const tauriWindow = window.__TAURI__?.window;
   if (tauriWindow?.getCurrentWindow) {
@@ -443,6 +447,18 @@ function groupedChangedFiles(files = []) {
   return order.map((status) => ({ status, files: groups.get(status) })).filter((group) => group.files.length);
 }
 
+function diffBinaryImagePreviewTemplate(diffResult) {
+  const mime = escapeHtml(diffResult.previewMime || "");
+  const b64 = diffResult.previewBase64 || "";
+  const caption = diffResult.diff ? escapeHtml(diffResult.diff) : "";
+  return `<div class="diff-preview diff-binary-image-panel">
+    <div class="diff-image-preview-frame">
+      <img class="diff-image-preview" alt="" decoding="async" src="data:${mime};base64,${b64}" />
+    </div>
+    ${caption ? `<pre class="diff-binary-caption">${caption}</pre>` : ""}
+  </div>`;
+}
+
 function diffTemplate(diffResult) {
   if (!diffResult) {
     return workflowEmptyStateTemplate({
@@ -452,6 +468,9 @@ function diffTemplate(diffResult) {
       actions: false,
     });
   }
+  if (diffResult.previewBase64 && diffResult.previewMime) {
+    return diffBinaryImagePreviewTemplate(diffResult);
+  }
   if (diffResult.isBinary) {
     return workflowEmptyStateTemplate({
       title: "Binary file",
@@ -928,6 +947,11 @@ function filePreviewTemplate(file) {
       <span class="muted">${escapeHtml(meta)}</span>
     </div>`;
 
+  if (file.previewBase64 && file.previewMime) {
+    const mime = escapeHtml(file.previewMime);
+    const b64 = file.previewBase64;
+    return `${header}<div class="viewer-image-preview-wrap"><img class="viewer-image-preview" alt="" decoding="async" src="data:${mime};base64,${b64}" /></div>`;
+  }
   if (file.tooLarge) {
     return header + `<div class="empty-state viewer-empty"><div>File too large to preview</div><div class="muted">Preview is limited to ${formatBytes(maxPreviewBytes)}.</div></div>`;
   }
@@ -1993,6 +2017,8 @@ async function openViewerFile(path) {
         content: file.content || "",
         isBinary: file.isBinary,
         tooLarge: file.tooLarge,
+        previewMime: file.previewMime,
+        previewBase64: file.previewBase64,
       };
     }
   } catch (error) {
@@ -2670,11 +2696,13 @@ function bindDashboardEvents() {
 
 function render() {
   applyTheme();
+  applyPlatformChrome();
   dashboardView();
 }
 
 window.addEventListener("DOMContentLoaded", async () => {
   applyTheme();
+  applyPlatformChrome();
   await loadRepositories();
   if (getState().selectedRepoPath) {
     await refreshRepoData();