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/campaign.rs

@@ -504,6 +504,7 @@ pub fn start_mission(i: usize, carry: Option<&Carry>) -> Game {
         g.add_rival(side, x, y, diff);
     }
     g.place_dwarf_caves(d.seed);
+    g.init_research(Some(i));
     let heart = d.gate || d.forts.iter().any(|f| f.heart);
     if !heart {
         g.gate_hp = 0.0;