gui: complete Wails v2 vertical MVP — fixes, search, polished UI

Backend fixes:
- Wire search service in App struct, implement Search() bindings
- Fix OpenFile to use files.Service.Open() instead of stub
- Fix OpenFolder to open spaces/<slug>/ instead of vault root
- Remove unused imports and dead code in app.go

Frontend fixes:
- Add missing Svelte plugin to vite.config.js (blocking build error)
- Fix optional catch binding for compatibility
- Fix select dropdown rendering on Linux (appearance: none + custom arrow)
- Switch api/verstak.js to use generated Wails v2 bindings
- Include hand-written wailsjs bindings in repository
- Add build.sh to repository

Build:
  cd frontend && npm run build
  rm -rf cmd/verstak-gui/frontend-dist && cp -r frontend/dist cmd/verstak-gui/frontend-dist
  go build -tags 'gui production webkit2_41' -o verstak-gui ./cmd/verstak-gui

frontend/src/wailsjs/go/main/App.js

@@ -0,0 +1,91 @@
+// @ts-check
+// Wails v2 generated bindings — auto-generated by wails build
+// Manual version for go build -tags gui
+
+export function ListSections() {
+    return window['go']['main']['App']['ListSections']();
+}
+
+export function ListNodesBySection(arg1) {
+    return window['go']['main']['App']['ListNodesBySection'](arg1);
+}
+
+export function ListChildren(arg1) {
+    return window['go']['main']['App']['ListChildren'](arg1);
+}
+
+export function GetNodeDetail(arg1) {
+    return window['go']['main']['App']['GetNodeDetail'](arg1);
+}
+
+export function CreateNode(arg1, arg2, arg3, arg4) {
+    return window['go']['main']['App']['CreateNode'](arg1, arg2, arg3, arg4);
+}
+
+export function DeleteNode(arg1) {
+    return window['go']['main']['App']['DeleteNode'](arg1);
+}
+
+export function ListNotes(arg1) {
+    return window['go']['main']['App']['ListNotes'](arg1);
+}
+
+export function CreateNote(arg1, arg2) {
+    return window['go']['main']['App']['CreateNote'](arg1, arg2);
+}
+
+export function ReadNote(arg1) {
+    return window['go']['main']['App']['ReadNote'](arg1);
+}
+
+export function SaveNote(arg1, arg2) {
+    return window['go']['main']['App']['SaveNote'](arg1, arg2);
+}
+
+export function ListFiles(arg1) {
+    return window['go']['main']['App']['ListFiles'](arg1);
+}
+
+export function ListActions(arg1) {
+    return window['go']['main']['App']['ListActions'](arg1);
+}
+
+export function RunAction(arg1) {
+    return window['go']['main']['App']['RunAction'](arg1);
+}
+
+export function ListWorklog(arg1) {
+    return window['go']['main']['App']['ListWorklog'](arg1);
+}
+
+export function CreateWorklog(arg1, arg2, arg3) {
+    return window['go']['main']['App']['CreateWorklog'](arg1, arg2, arg3);
+}
+
+export function Search(arg1) {
+    return window['go']['main']['App']['Search'](arg1);
+}
+
+export function PickFile() {
+    return window['go']['main']['App']['PickFile']();
+}
+
+export function PickFiles() {
+    return window['go']['main']['App']['PickFiles']();
+}
+
+export function PickDirectory() {
+    return window['go']['main']['App']['PickDirectory']();
+}
+
+export function OpenFile(arg1) {
+    return window['go']['main']['App']['OpenFile'](arg1);
+}
+
+export function OpenFolder(arg1) {
+    return window['go']['main']['App']['OpenFolder'](arg1);
+}
+
+export function VerstakVersion() {
+    return window['go']['main']['App']['VerstakVersion']();
+}