Build menu: traps, doors, steel walls and siege engines; new tools unlock by mission

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

lang/en.lang

@@ -884,7 +884,7 @@ room.forge = Forge
 tool.forge.label = Forge
 tool.forge.desc = Creatures manufacture traps and doors here - work, no gold. Finished pieces wait in crates until an imp installs them. Coglings come for a forge of 6+ tiles.
 unit.cogling = Cogling
-cat.traps = Traps
+cat.traps = Build
 cost.work = {0} work in the forge
 job.forge = Forging
 job.install = Installing a trap