Give Effector a version and a changelog, shown from the menu

The version is the project() line of CMakeLists.txt and nowhere else:
CMake writes it, with the text of CHANGELOG.md, into a generated
core/version.hpp, so the number and the release notes the binary shows
are the ones it was built from. effector --version (-V) prints it, and
the header-bar menu gains a section with Changelog, a window laying the
Markdown out as headings and bullets, and About Effector.

The core tests hold the newest changelog entry to the current version,
so a bump cannot go in without its notes. Releases are tagged vX.Y.Z;
this is 0.5.0, and the changelog reconstructs 0.1.0-0.4.0 from the
history.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/cli/options.cpp

@@ -61,6 +61,8 @@ Options parseOptions(int argc, char** argv) {
 
         if (arg == "-h" || arg == "--help") {
             options.showHelp = true;
+        } else if (arg == "-V" || arg == "--version") {
+            options.showVersion = true;
         } else if (arg == "--list-effects") {
             options.listEffects = true;
         } else if (arg == "-e" || arg == "--effect") {
@@ -184,6 +186,7 @@ std::string usage(const char* programName) {
         << "      --disable NAME    keep this effect in the chain but skip it\n"
         << "      --seed N          random seed (default: random)\n"
         << "      --list-effects    list available effects and exit\n"
+        << "  -V, --version         show the version and exit\n"
         << "  -h, --help            show this help and exit\n";
 
     out << "\nCanvas formats (--format):\n";

src/cli/options.hpp

@@ -27,6 +27,7 @@ struct Options {
     ParamValues params;              // only the keys the user actually passed
     bool listEffects = false;
     bool showHelp = false;
+    bool showVersion = false;
 };
 
 // Throws EffectError on bad input. Effect flags are generated from the