Include actor.h from controller.h so the header compiles on its own

controller.h declares three handler pointers taking an akgl_Actor * and
included nothing that declares that type, so any translation unit reaching
for it before akgl/actor.h failed with "unknown type name 'akgl_Actor'".
src/controller.c never noticed because it includes akgl/game.h first, and
tests/controller.c carried a comment explaining the workaround.

Included rather than forward-declared: akgl_Actor is a typedef of a named
struct and repeating a typedef is C11, not C99. It closes no cycle --
actor.h reaches only types.h and character.h.

tests/headers.c is a whole suite for one #include on purpose. A second
#include after the first proves nothing about the second, because by then
the first has dragged its dependencies in; covering another header means
another file shaped like this one.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/headers.c

@@ -0,0 +1,37 @@
+/**
+ * @file headers.c
+ * @brief Checks that a public header can be the first thing a caller includes.
+ *
+ * The assertion here is the compile, not anything main() does. `akgl/controller.h`
+ * declares its binding handlers as taking an `akgl_Actor *` and once did not
+ * declare that type, so every translation unit that reached for it before
+ * `akgl/actor.h` failed with "unknown type name 'akgl_Actor'". `src/controller.c`
+ * never noticed, because it includes `akgl/game.h` first.
+ *
+ * One header per file, deliberately. A second `#include` after the first proves
+ * nothing about the second: by then the first has already dragged its
+ * dependencies in. Covering another header means another file like this one.
+ */
+
+#include <akgl/controller.h>
+
+#include <string.h>
+
+int main(void)
+{
+    akgl_Control control;
+
+    // Enough to require the akgl_Actor declaration to be complete rather than
+    // merely present: the handler signature names it, and a control map holds
+    // one by value.
+    memset(&control, 0x00, sizeof(akgl_Control));
+    control.key = SDLK_LEFT;
+    control.handler_on = &akgl_Actor_cmhf_left_on;
+    if ( control.handler_on == NULL ) {
+	return 1;
+    }
+    if ( sizeof(GAME_ControlMaps) != (sizeof(akgl_ControlMap) * AKGL_MAX_CONTROL_MAPS) ) {
+	return 1;
+    }
+    return 0;
+}