Research in the library: rooms, spells, towers, traps and doors are discovered in a fixed order

- studying creatures collect research points (mages and owls best, higher levels faster); studying gives less mana than before
- free play starts with the basics; campaign missions know what their story allows and can research what the next four missions would bring
- research shown in the top bar; the library's info lists the current item and what comes next; locked tools say whether they can be researched

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

src/main.rs

@@ -14,6 +14,7 @@ mod menu;
 mod platform;
 mod particles;
 mod props;
+mod research;
 mod rival;
 mod render3d;
 mod save;
@@ -862,7 +863,8 @@ async fn main() {
                     }
                     UiAction::OpenMenu => menu.page = Some(Page::Pause),
                     UiAction::Locked => {
-                        app.game.msg("msg.tool_locked", vec![]);
+                        let locked = ui.last_locked.unwrap_or(usize::MAX);
+                        app.game.msg(if app.game.can_research(locked) { "msg.tool_research" } else { "msg.tool_locked" }, vec![]);
                         app.game.sfx_ui(game::Sfx::Error);
                     }
                     UiAction::CloseHelp | UiAction::SelectLanguage(_) | UiAction::Consumed => {}