feat(ui): add show in file manager button to screenshot view

- Add Tools::open_file_manager helper with Windows and Linux support.
- Ensure screenshot directory is created before scanning.
- Add localization keys for en_US and zh_CN.

include/Cubed/tools/file_utils.hpp

@@ -0,0 +1,57 @@
+#pragma once
+#include "Cubed/tools/log.hpp"
+
+#include <filesystem>
+#include <string>
+
+#ifdef _WIN32
+// clang-format off
+#include <windows.h>
+#include <shellapi.h>
+// clang-format on
+#elif __linux__
+#include <cstdlib>
+#endif
+
+namespace Cubed::Tools {
+
+inline void open_file_manager(const std::filesystem::path& path) {
+#ifdef _WIN32
+
+    ShellExecuteW(nullptr, L"open", path.wstring().c_str(), nullptr, nullptr,
+                  SW_SHOWNORMAL);
+
+#elif __linux__
+
+    constexpr const char* FILE_MANAGERS[] = {"nautilus", "dolphin", "thunar",
+                                             "nemo", "pcmanfm"};
+
+    auto is_available = [](const char* exe) {
+        std::string cmd = std::string("command -v ") + exe + " >/dev/null 2>&1";
+        return std::system(cmd.c_str()) == 0;
+    };
+
+    const std::string QUOTED = "\"" + path.string() + "\"";
+    for (const char* fm : FILE_MANAGERS) {
+        if (!is_available(fm)) {
+            continue;
+        }
+        std::string cmd = std::string(fm) + " " + QUOTED + " >/dev/null 2>&1 &";
+        if (std::system(cmd.c_str()) == 0) {
+            return;
+        }
+    }
+
+    // Fallback: let the system choose a handler.
+    if (is_available("xdg-open")) {
+        std::string cmd = "xdg-open " + QUOTED + " >/dev/null 2>&1 &";
+        if (std::system(cmd.c_str()) == 0) {
+            return;
+        }
+    }
+
+    Logger::warn("Failed to open file manager for {}", path.string());
+#endif
+}
+
+} // namespace Cubed::Tools