Namespace every exported symbol, and bump to 0.5.0

Closes internal-consistency items 1 through 6, 12 and 13. Every include guard
is _AKGL_<FILE>_H_, every in-project header include is angled, and every
exported function, type and global carries the akgl_ prefix. This is an ABI
break; the soname goes to libakgl.so.0.5. TODO.md carries the full rename
table.

The renames were driven by renaming each declaration and letting the compiler
find the uses, not by pattern substitution: renderer, physics and camera are
also parameter and struct-member names, and a sed would have rewritten
map->physics and every akgl_RenderBackend *renderer parameter without a word.

Item 4 turned out not to be cosmetic. The library exported a global called
renderer and tests/character.c defined an SDL_Renderer *renderer of its own;
the executable's definition preempted the library's, akgl_sprite_load_json
read a SDL_Renderer * through an akgl_RenderBackend *, and every texture load
in that suite failed. The suite reported success anyway, because libakerror's
unhandled-error handler ends in exit(errctx->status), exit keeps only the low
byte, and AKGL_ERR_SDL is exactly 256. So character had been green while
running one of its four tests, and every suite in the tree was unable to fail
on the most common status in a library built on SDL.

Both are fixed. tests/testutil.h gains TEST_TRAP_UNHANDLED_ERRORS(), which
collapses any status a byte cannot carry onto 1, and every suite installs it.
character binds a real backend with akgl_render_2d_bind. Its fourth test then
runs for the first time and fails on a defect it has asserted all along, so
akgl_heap_release_character now walks state_sprites with
AKGL_ITERATOR_OP_RELEASE and destroys the property set before zeroing the slot
-- TODO.md Defects item 21 and half of Carried over item 1.

AKGL_TIME_ONESEC_MS said "one second in milliseconds" and held 1000000, so
akgl_game_state_lock waited roughly sixteen minutes rather than one second. It
is AKGL_TIME_ONEMS_NS now, the budget is its own named constant, and
tests/game.c holds the mutex from a second thread to assert the wait -- the
contended path had no coverage at all.

Headers are self-contained and it is enforced: AKGL_PUBLIC_HEADERS drives both
install() and a generated translation unit per header, so a header that ships
is a header that is checked. Writing that found registry.h, which used
SDL_PropertiesID in eight declarations and included no SDL header.

23/23 suites pass, memcheck is clean, reindent --check is clean.

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

include/akgl/sprite.h

@@ -12,7 +12,7 @@
  * both publish themselves in a registry under their name, which is how
  * akgl_character_sprite_add and the tilemap loader find them. Because loading a
  * sheet uploads a texture, the renderer has to exist first -- so
- * akgl_render_init2d, or akgl_game_init, before any of this.
+ * akgl_render_2d_init, or akgl_game_init, before any of this.
  */
 
 #ifndef _AKGL_SPRITE_H_
@@ -47,7 +47,7 @@ typedef struct {
     uint32_t frames;                            /**< How many entries of frameids are in use. */
     uint32_t width;                             /**< Frame width in pixels; also the horizontal stride used to find a frame on the sheet. */
     uint32_t height;                            /**< Frame height in pixels; the vertical stride once frames wrap to the next row. */
-    uint32_t speed;                             /**< Nanoseconds one frame is held. Read from JSON in milliseconds and scaled by #AKGL_TIME_ONESEC_MS, which despite its name is nanoseconds-per-millisecond. TODO.md item 6. */
+    uint32_t speed;                             /**< Nanoseconds one frame is held. Read from JSON in milliseconds and scaled by #AKGL_TIME_ONEMS_NS. */
     bool loop;                                  /**< Restart from frame 0 when the last frame is reached, instead of holding it. */
     bool loopReverse;                           /**< Play back down to frame 0 instead of jumping to it -- a ping-pong loop. */
     char name[AKGL_SPRITE_MAX_NAME_LENGTH];     /**< Registry key, from the JSON `name` field. */
@@ -82,7 +82,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_sprite_initialize(akgl_Sprite *spr, char
 /**
  * @brief Load an image file as a texture and publish it as a spritesheet.
  *
- * Uploads @p filename through SDL_image using the global `renderer`, so the
+ * Uploads @p filename through SDL_image using the global `akgl_renderer`, so the
  * renderer must already be initialized. The sheet is registered in
  * #AKGL_REGISTRY_SPRITESHEET under @p filename, which is the key
  * akgl_sprite_load_json looks it up by to avoid loading the same image twice.
@@ -166,6 +166,6 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_sprite_load_json(char *filename);
  *         `NULL`. Note that `sheet->texture` is dereferenced without a check,
  *         so a registered-but-unloaded sheet is a crash rather than an error.
  */
-akerr_ErrorContext *akgl_sprite_sheet_coords_for_frame(akgl_Sprite *self, SDL_FRect *srccoords, uint8_t frameid);
+akerr_ErrorContext *akgl_spritesheet_coords_for_frame(akgl_Sprite *self, SDL_FRect *srccoords, uint8_t frameid);
 
 #endif //_AKGL_SPRITE_H_