Release 1.0.0: rename to NoMines, add leaderboard, theme support and release metadata

- Rename app/binary/app-id to nomines (io.github.bemagri.nomines), config dir
  moves to ~/.config/nomines with legacy path fallback
- Add persistent best-time leaderboard (Glib::KeyFile)
- Theme-aware board following system light/dark preference
- Beveled 3D cells, confetti win animation, keyboard shortcuts,
  right-click chording, per-difficulty window sizing
- Add AppStream metainfo, validate desktop file and metainfo via meson tests
- Fix license metadata to GPL-3.0-or-later and real homepage

src/leaderboard.hpp

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <map>
+#include <optional>
+#include <string>
+
+// Persistent best times, stored as a GKeyFile under the user config dir:
+// ~/.config/minesweeper/leaderboard.ini  (gitignored)
+class Leaderboard {
+public:
+    // Records a finished game. Returns true when it is a new best time
+    // for the difficulty; the file is saved immediately.
+    bool record(const std::string& difficulty, int seconds);
+
+    // Best time in seconds for the difficulty, if one exists.
+    std::optional<int> best_time(const std::string& difficulty) const;
+
+private:
+    void load();
+    void save();
+
+    std::map<std::string, int> times_;
+    bool loaded_ = false;
+};