Eight new spells: seer's eye, cave-in, haste, stoneskin, gold rain, invisibility, plague, quake

- researched in the library (and unlocked in the campaign), in the spells menu with own icons and a radius under the pointer
- haste speeds up everything a creature does, stoneskin halves damage, invisible creatures are ignored by enemies and towers until they attack (drawn see-through), plague spreads among enemies, quake hurts and stuns enemies only, cave-in turns floor back into earth
- particles for every spell

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

src/research.rs

@@ -9,23 +9,31 @@ use crate::game::*;
 pub const RESEARCH: &[(usize, f32)] = &[
     (5, 200.0),   // training hall
     (10, 250.0),  // heal
+    (34, 250.0),  // haste
     (21, 300.0),  // forge
     (22, 250.0),  // spike pit
     (29, 250.0),  // wooden door
+    (32, 300.0),  // seer's eye
     (15, 400.0),  // cannon tower
     (12, 450.0),  // torture chamber
     (26, 300.0),  // alarm bell
+    (35, 400.0),  // stoneskin
     (11, 500.0),  // summon
     (13, 550.0),  // temple
     (23, 500.0),  // poison vent
     (30, 500.0),  // iron door
+    (33, 550.0),  // cave-in
     (18, 550.0),  // aerie
     (16, 650.0),  // magic tower
+    (36, 600.0),  // gold rain
     (24, 650.0),  // fire jet
     (25, 650.0),  // stone roller
+    (37, 700.0),  // invisibility
     (19, 700.0),  // steel walls
     (28, 800.0),  // frost glow
+    (38, 850.0),  // plague
     (27, 900.0),  // rune mine
+    (39, 950.0),  // quake
     (31, 1100.0), // magic door
 ];