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.cpp

@@ -0,0 +1,67 @@
+#include "leaderboard.hpp"
+#include <glibmm/fileutils.h>
+#include <glibmm/keyfile.h>
+#include <glibmm/miscutils.h>
+#include <glib.h>
+
+namespace {
+std::string file_path() {
+    return Glib::build_filename(
+        Glib::get_user_config_dir(), "nomines", "leaderboard.ini");
+}
+} // namespace
+
+void Leaderboard::load() {
+    if (loaded_) return;
+    loaded_ = true;
+
+    // Migrate scores from pre-1.0 builds that stored them under minesweeper/
+    auto path = file_path();
+    auto legacy = Glib::build_filename(
+        Glib::get_user_config_dir(), "minesweeper", "leaderboard.ini");
+    if (!Glib::file_test(path, Glib::FileTest::EXISTS) &&
+        Glib::file_test(legacy, Glib::FileTest::EXISTS)) {
+        path = legacy;
+    }
+
+    try {
+        auto kf = Glib::KeyFile::create();
+        kf->load_from_file(path);
+        for (const auto& group : kf->get_groups()) {
+            if (kf->has_key(group, "best")) {
+                times_[group.raw()] = kf->get_integer(group, "best");
+            }
+        }
+    } catch (const Glib::Error&) {
+        // No file yet or unreadable — start with an empty leaderboard
+    }
+}
+
+bool Leaderboard::record(const std::string& difficulty, int seconds) {
+    load();
+    auto it = times_.find(difficulty);
+    if (it != times_.end() && it->second <= seconds) return false;
+    times_[difficulty] = seconds;
+    save();
+    return true;
+}
+
+std::optional<int> Leaderboard::best_time(const std::string& difficulty) const {
+    auto it = times_.find(difficulty);
+    if (it == times_.end()) return std::nullopt;
+    return it->second;
+}
+
+void Leaderboard::save() {
+    auto kf = Glib::KeyFile::create();
+    for (const auto& [difficulty, seconds] : times_) {
+        kf->set_integer(difficulty, "best", seconds);
+    }
+    try {
+        auto dir = Glib::path_get_dirname(file_path());
+        g_mkdir_with_parents(dir.c_str(), 0700);
+        kf->save_to_file(file_path());
+    } catch (const Glib::Error&) {
+        // Best-effort persistence; a failed save is not fatal
+    }
+}