Consume libakgl 0.3.0: every workaround deleted, two capabilities gained

0.3.0 closed all ten API gaps this port had filed. The four workarounds go
with them: the CMake block that declared libakgl's vendored dependencies by
hand, the akgl/actor.h include in three files, and the six vtable pointers
assigned by hand in two more, now akgl_render_bind2d().

Two gaps were capabilities rather than inconveniences, and both are now real:

The line editor takes the composed UTF-8 text the ring carries in preference
to the keycode, so shifted characters, keyboard layouts, compose keys and dead
keys all work. A double quote can be typed, which means a BASIC string literal
can be typed -- the sharp end of the old limitation. Letters are no longer
folded to upper case.

SOUND's dir/min/step reach akgl_audio_sweep instead of being refused. dir 3
sweeps once rather than oscillating and TODO.md section 5 says so. A backend
with no sweep still refuses the swept note and plays the held one.

The adaptors now carry an AKGL_VERSION_AT_LEAST(0, 3, 0) floor, verified by
temporarily demanding 0.4.0 and watching it fire.

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

src/input_akgl.c

@@ -16,15 +16,6 @@
 
 #include <akerror.h>
 
-/*
- * akgl/actor.h before akgl/controller.h, and it is not optional: controller.h
- * declares two handler function pointers taking an akgl_Actor * and includes
- * nothing that declares the type, so on its own it does not compile. Not a
- * workaround anybody should copy -- filed upstream against libakgl, whose own
- * style rules call for self-contained headers. Delete this note and the include
- * when controller.h includes what it uses.
- */
-#include <akgl/actor.h>
 #include <akgl/controller.h>
 #include <akgl/error.h>