refactor: src-tauri 重命名为 gui

Tauri CLI 自动检测 workspace 成员，构建不受影响。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

gui/src/commands/scanner.rs

@@ -0,0 +1,6 @@
+use path_editor_core::scanner;
+
+#[tauri::command]
+pub fn scan_conflicts(paths: Vec<String>) -> Result<Vec<scanner::ConflictEntry>, String> { scanner::scan_conflicts(paths) }
+#[tauri::command]
+pub fn scan_tools(paths: Vec<String>, query: String) -> Result<Vec<scanner::ToolGroup>, String> { scanner::scan_tools(paths, query) }