Raise walls: plan them on own floor, imps build reinforced earth

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

src/research.rs

@@ -45,7 +45,7 @@ pub const RESEARCH: &[(usize, f32)] = &[
 ];
 
 // known from the start in free play
-pub const BASE_TOOLS: &[usize] = &[0, 1, 2, 3, 4, 6, 7, 8, 9, 14, 17, 20, 45, 46];
+pub const BASE_TOOLS: &[usize] = &[0, 1, 2, 3, 4, 6, 7, 8, 9, 14, 17, 20, 45, 46, 49];
 
 // campaign: what the next missions bring may be researched early
 const LOOKAHEAD: usize = 4;