Give every exported function a declaration, and check that it stays that way

Closes internal-consistency items 7 through 15. Nineteen non-static functions
were in the ABI with no declaration anywhere, so no consumer could call them
and any consumer could collide with them.

The four gamepad_handle_* functions are the ones that mattered: controller.h
declared akgl_controller_handle_button_down and three siblings that did not
exist, so anything compiled against the header alone failed to link. The
definitions carry the declared names now, which also closes Defects -> Known
and still open item 10, and their documentation moved to the header.

The rest are either declared under a "part of the internal API" block --
akgl_game_save_actors and akgl_game_load_versioncmp, which tests/game.c had to
declare for itself, plus six tilemap loader helpers the untested-loader work
wants to reach -- or static, which is what the four save iterators and
load_objectnamemap should always have been. akgl_path_relative_from is deleted:
declared nowhere, called from nowhere, never wrote its output, and leaked a
pooled string on every call, so it closes Known and still open item 4 and item
40 by ceasing to exist.

scripts/check_api_surface.sh keeps it closed. It reads the built library's
dynamic symbol table and every public header with comments stripped, and fails
on an exported akgl_* symbol that is declared nowhere. Stripping comments is
the whole point -- four of these were mentioned in controller.h prose, which is
how they went unnoticed.

The pool-size ceilings are defined once, in heap.h, so the #ifndef override
hook fires for the first time; actor.h, sprite.h and character.h were defining
the same four unconditionally from headers heap.h includes above its own guard.
tests/header_pool_override.c fails the compile if that regresses.

Also here: (void) rather than () on the twelve no-argument entry points,
AKERR_NOIGNORE only on declarations, static helpers with the akgl_ prefix
dropped, and the six parameter-name mismatches. akgl_get_json_with_default had
its two contexts swapped rather than merely misspelled -- the incoming one was
`err` and its own was `e`, which is the name reserved for an incoming one.

24/24 pass, reindent --check clean.

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

src/audio.c

@@ -283,7 +283,7 @@ static void SDLCALL audio_stream_callback(void *userdata, SDL_AudioStream *strea
     }
 }
 
-akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_init(void)
+akerr_ErrorContext *akgl_audio_init(void)
 {
     SDL_AudioSpec spec;
 
@@ -322,7 +322,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_init(void)
     SUCCEED_RETURN(errctx);
 }
 
-akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_shutdown(void)
+akerr_ErrorContext *akgl_audio_shutdown(void)
 {
     SDL_AudioStream *closing = audiostream;
 
@@ -337,7 +337,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_shutdown(void)
     SUCCEED_RETURN(errctx);
 }
 
-akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_tone(int voice, float32_t hz, uint32_t ms)
+akerr_ErrorContext *akgl_audio_tone(int voice, float32_t hz, uint32_t ms)
 {
     PREPARE_ERROR(errctx);
     PASS(errctx, check_voice(voice));
@@ -350,7 +350,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_tone(int voice, float32_t hz, uint
     SUCCEED_RETURN(errctx);
 }
 
-akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_sweep(int voice, float32_t from_hz, float32_t to_hz, float32_t step_hz, uint32_t ms)
+akerr_ErrorContext *akgl_audio_sweep(int voice, float32_t from_hz, float32_t to_hz, float32_t step_hz, uint32_t ms)
 {
     PREPARE_ERROR(errctx);
     PASS(errctx, check_voice(voice));
@@ -368,7 +368,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_sweep(int voice, float32_t from_hz
     SUCCEED_RETURN(errctx);
 }
 
-akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_stop(int voice)
+akerr_ErrorContext *akgl_audio_stop(int voice)
 {
     PREPARE_ERROR(errctx);
     PASS(errctx, check_voice(voice));
@@ -382,7 +382,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_stop(int voice)
     SUCCEED_RETURN(errctx);
 }
 
-akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_waveform(int voice, akgl_AudioWaveform waveform)
+akerr_ErrorContext *akgl_audio_waveform(int voice, akgl_AudioWaveform waveform)
 {
     PREPARE_ERROR(errctx);
     PASS(errctx, check_voice(voice));
@@ -401,7 +401,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_waveform(int voice, akgl_AudioWave
     SUCCEED_RETURN(errctx);
 }
 
-akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_envelope(int voice, uint32_t attack, uint32_t decay, float32_t sustain, uint32_t release)
+akerr_ErrorContext *akgl_audio_envelope(int voice, uint32_t attack, uint32_t decay, float32_t sustain, uint32_t release)
 {
     PREPARE_ERROR(errctx);
     PASS(errctx, check_voice(voice));
@@ -422,7 +422,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_envelope(int voice, uint32_t attac
     SUCCEED_RETURN(errctx);
 }
 
-akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_volume(float32_t level)
+akerr_ErrorContext *akgl_audio_volume(float32_t level)
 {
     PREPARE_ERROR(errctx);
     FAIL_NONZERO_RETURN(
@@ -439,7 +439,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_volume(float32_t level)
     SUCCEED_RETURN(errctx);
 }
 
-akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_voice_active(int voice, bool *active)
+akerr_ErrorContext *akgl_audio_voice_active(int voice, bool *active)
 {
     PREPARE_ERROR(errctx);
     PASS(errctx, check_voice(voice));
@@ -452,7 +452,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_voice_active(int voice, bool *acti
     SUCCEED_RETURN(errctx);
 }
 
-akerr_ErrorContext AKERR_NOIGNORE *akgl_audio_mix(float32_t *dest, int frames)
+akerr_ErrorContext *akgl_audio_mix(float32_t *dest, int frames)
 {
     akgl_AudioVoice *voice = NULL;
     float32_t sum = 0.0f;