fix(input): reset controls on focus loss

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/engine/input_focus_reset_test.lua

@@ -0,0 +1,24 @@
+-- Focus / visibility loss clears held directions (SWNX-18).
+package.path = "./?.lua;./?/init.lua;" .. package.path
+if not _G.love then _G.love = require("tests.love_stub") end
+
+local T = require("tests.harness")
+local check = T.check
+
+local Input = require("src.core.Input")
+local Game = require("src.core.Game")
+
+Input:init()
+Input:keypressed("left")
+Input:step()
+check(Input:isDown("left"), "left held before focus loss")
+
+Game:focus(false)
+check(not Input:isDown("left"), "focus loss clears held direction")
+
+Input:keypressed("up")
+Input:step()
+Game:visible(false)
+check(not Input:isDown("up"), "visibility loss clears held direction")
+
+T.finish()