Refactor: ES module architecture, tauri-plugin-store, unified design

Major changes:
- ES module system: main.js as central hub, shared modules
- tauri-plugin-store for persistent storage (dialog, fs plugins added)
- tauri-plugin-dialog for folder selection
- tauri-plugin-fs for real file system scanning
- Removed MOCK_FILES/FILE_TREE - real file scanner implemented
- All pages use unified page-header + page-content layout
- Custom titlebar with window controls
- Onboarding: 4-step flow with folder selection (Downloads default)
- CSS: unified design system, .hidden utility class added
- SVG icons throughout (no emoji)

Note: onboarding.js downloadDir() has runtime issue - needs fix

src-tauri/Cargo.toml

@@ -23,3 +23,6 @@ serde = { version = "1.0", features = ["derive"] }
 log = "0.4"
 tauri = { version = "2.11.2", features = [] }
 tauri-plugin-log = "2"
+tauri-plugin-store = "2"
+tauri-plugin-dialog = "2"
+tauri-plugin-fs = "2"

src-tauri/capabilities/default.json

@@ -6,6 +6,17 @@
     "main"
   ],
   "permissions": [
-    "core:default"
+    "core:default",
+    "core:window:default",
+    "core:window:allow-close",
+    "core:window:allow-minimize",
+    "core:window:allow-toggle-maximize",
+    "core:window:allow-is-maximized",
+    "core:window:allow-start-dragging",
+    "store:default",
+    "dialog:default",
+    "fs:default",
+    "fs:allow-read-dir",
+    "fs:allow-stat"
   ]
-}
+}

src-tauri/src/lib.rs

@@ -1,6 +1,10 @@
 #[cfg_attr(mobile, tauri::mobile_entry_point)]
 pub fn run() {
   tauri::Builder::default()
+    .plugin(tauri_plugin_store::Builder::new().build())
+    .plugin(tauri_plugin_log::Builder::default().build())
+    .plugin(tauri_plugin_dialog::init())
+    .plugin(tauri_plugin_fs::init())
     .run(tauri::generate_context!())
     .expect("error while running tauri application");
 }

src-tauri/tauri.conf.json

@@ -20,7 +20,9 @@
         "minHeight": 600,
         "center": true,
         "resizable": true,
-        "fullscreen": false
+        "fullscreen": false,
+        "decorations": false,
+        "transparent": true
       }
     ],
     "security": {
@@ -28,7 +30,7 @@
     }
   },
   "bundle": {
-    "active": true,
+    "active": false,
     "targets": "all",
     "icon": [
       "icons/32x32.png",