Add external editor/file picker, update theme

Introduce file/application pickers and external-editor integration, plus a visual refresh. Frontend: add UI for selecting/rescanning installed IDEs, custom editor input, "Open in File Explorer" and "Open in Code Editor" actions, clone destination browse, helper utilities, new icons, and many CSS theme/UX improvements (variables, shadows, scrollbars, selection, refined component styles). State: track installedIdes and scan status. Tauri API: expose browseDirectory, browseApplication and scanInstalledIdes, and wire UI handlers to call them. Backend: add InstalledIde struct and update tauri Cargo manifest and capabilities to allow dialogs. Overall improves editor/workflow integrations and modernizes the app styling.

frontend/js/tauri-api.js

@@ -1,4 +1,5 @@
 const invoke = window.__TAURI__?.core?.invoke;
+const dialog = window.__TAURI__?.dialog;
 
 function ensureInvoke() {
   if (!invoke) {
@@ -6,6 +7,33 @@ function ensureInvoke() {
   }
 }
 
+function ensureDialog() {
+  if (!dialog?.open) {
+    throw new Error("Tauri dialog API is not available.");
+  }
+}
+
+export async function browseDirectory(defaultPath = "") {
+  ensureDialog();
+  return dialog.open({
+    directory: true,
+    multiple: false,
+    defaultPath: defaultPath || undefined,
+  });
+}
+
+export async function browseApplication(defaultPath = "") {
+  ensureDialog();
+  return dialog.open({
+    directory: false,
+    multiple: false,
+    defaultPath: defaultPath || undefined,
+    filters: [
+      { name: "Applications", extensions: ["exe", "cmd", "bat", "app"] },
+    ],
+  });
+}
+
 export async function runGitClone(repoUrl, destinationPath, gitPath) {
   ensureInvoke();
   return invoke("git_clone", {
@@ -131,6 +159,11 @@ export async function openInExternalEditor(repoPath, editorPath) {
   return invoke("open_in_external_editor", { repoPath, editorPath });
 }
 
+export async function scanInstalledIdes() {
+  ensureInvoke();
+  return invoke("scan_installed_ides");
+}
+
 export async function scanLocalRepos(roots = [], allowedRemoteUrls = [], gitPath = "", maxDepth = 4, maxResults = 200) {
   ensureInvoke();
   return invoke("scan_local_repos", {