feat(input-test): migrate to test-lib (manifest.lib + run_tests) (Test-Opt Phase 3.2)

Per ADR-0037 Tests-as-Libs Convention. Renamed on Gitea + moved
locally. History preserved.

init.lua

@@ -4,7 +4,9 @@
 
 local input = require("lib-core.input")
 
-function init(ctx)
+local M = {}
+
+function M.run_tests(ctx)
     -- Engine surface present (7 assertions)
     engine.test.assert(type(engine.input.MOUSE_LEFT)   == "number",
                        "MOUSE_LEFT constant is integer")
@@ -52,3 +54,5 @@ function init(ctx)
     engine.test.equals(input.action_count(), 3,
                        "key-only bind still works after BIND_MAP refactor")
 end
+
+return M