feat(help): open a generated command reference instead of Discussions (#1049)

HELP now opens docs/command-reference.md on GitHub — a 600-command
reference grouped by category with default shortcuts and selection
behavior, generated from the in-repo command registry. A staleness
test fails when the registry and the page drift apart; regenerate
with UPDATE_COMMAND_REFERENCE=1 cargo test command_reference. The
command-line notice is localized in all 21 languages.

src/locale_catalog.rs

@@ -1884,6 +1884,7 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "Opening \"{name}\" ({size_label})…" => Some(("common", "opening-name-size-label")),
         "Opening OCS Discussions for help and questions..." => Some(("view", "opening-ocs-discussions-for-help-and-questions")),
         "Opening OCS Web..." => Some(("view", "opening-ocs-web")),
+        "Opening the command reference..." => Some(("view", "opening-the-command-reference")),
         "Opening Patreon page..." => Some(("view", "opening-patreon-page")),
         "Opening feedback page..." => Some(("view", "opening-feedback-page")),
         "Opening file" => Some(("ui", "opening-file")),