Steel walls: plate earth walls next to own ground with steel

- New tool Steel (key O, orders category; campaign from mission 11): 80 gold per earth wall,
  40 for a reinforced wall; riveted iron plate texture
- Heroes dig through steel 20 times slower than through earth and avoid it (path cost 300)
- Selling turns a steel wall back into a reinforced wall and refunds half the plating
- Texts EN/DE, test

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

src/main.rs

@@ -68,7 +68,7 @@ struct Input {
 // Tile under the pointer for a tool: digging (and the hand) aim at walls too,
 // building and everything else only at the floor below the pointer
 fn tool_tile(cam: &Cam, map: &map::Map, tool: Tool, mx: f32, my: f32) -> Option<(i32, i32)> {
-    if matches!(tool, Tool::Dig | Tool::Hand) {
+    if matches!(tool, Tool::Dig | Tool::Hand | Tool::Steel) {
         return cam.pick_tile(map, mx, my).map(|(x, z, _)| (x, z));
     }
     let p = cam.ground_point(mx, my);
@@ -81,7 +81,7 @@ fn tool_tile(cam: &Cam, map: &map::Map, tool: Tool, mx: f32, my: f32) -> Option<
 }
 
 fn area_tool(t: Tool) -> bool {
-    matches!(t, Tool::Dig | Tool::Room(_) | Tool::Sell | Tool::Bridge)
+    matches!(t, Tool::Dig | Tool::Room(_) | Tool::Sell | Tool::Bridge | Tool::Steel)
 }
 
 // Use the active tool on the world at (mx, my) (CSS pixels): a click, or a tap on touch screens
@@ -94,7 +94,7 @@ fn world_action(app: &mut App, ui: &mut Ui, r3d: &R3d, inp: &mut Input, mx: f32,
     let ground = app.cam.ground_point(mx, my);
     let (wx, wy) = (ground.x, ground.y);
     match (ui.tool, tile) {
-        (Tool::Dig | Tool::Room(_) | Tool::Sell | Tool::Bridge, Some(t)) => inp.ldown = Some(t),
+        (Tool::Dig | Tool::Room(_) | Tool::Sell | Tool::Bridge | Tool::Steel, Some(t)) => inp.ldown = Some(t),
         (Tool::Hand, _) => {
             let j = r3d.pick_ent(&app.game, &app.cam, mx, my, false);
             if slap {
@@ -127,6 +127,7 @@ fn finish_rect(app: &mut App, tool: Tool, start: (i32, i32), mx: f32, my: f32) {
         Tool::Room(r) => app.game.build_rect(r, sx, sy, ex, ey),
         Tool::Sell => app.game.sell_rect(sx, sy, ex, ey),
         Tool::Bridge => app.game.build_bridges(sx, sy, ex, ey),
+        Tool::Steel => app.game.build_steel(sx, sy, ex, ey),
         _ => {}
     }
 }
@@ -900,6 +901,7 @@ fn draw_frame(app: &mut App, gfx: &Gfx, r3d: &mut R3d, ui: &mut Ui, menu: &mut M
         Tool::Heal => (Color::new(0.4, 1.0, 0.5, 1.0), Some((ground.x, ground.y, 2.55))),
         Tool::Summon => (Color::new(0.8, 0.5, 1.0, 1.0), None),
         Tool::Bridge => (Color::new(0.9, 0.7, 0.4, 1.0), None),
+        Tool::Steel => (Color::new(0.75, 0.8, 0.9, 1.0), None),
         Tool::Tower(_) => (Color::new(1.0, 0.6, 0.25, 1.0), None),
     };
     let ov = Overlay {