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>

CMakeLists.txt

@@ -2,7 +2,7 @@ cmake_minimum_required(VERSION 3.10)
 # The single source of truth for the library version. It drives the generated
 # include/akgl/version.h, the shared library's VERSION and SOVERSION, and the
 # Version field in akgl.pc. Bump it here and nowhere else.
-project(akgl VERSION 0.4.0 LANGUAGES C)
+project(akgl VERSION 0.5.0 LANGUAGES C)
 
 # Memory checking reuses the suites that already exist -- `ctest -T memcheck`
 # runs every registered test under valgrind -- rather than adding programs of its
@@ -154,6 +154,34 @@ if(NOT TARGET jansson::jansson)
   find_package(jansson)
 endif()
 
+# Every header installed into include/akgl/, by base name. This list is the
+# single source of truth for two things that must not drift apart: what gets
+# installed, and what the `headers` suite proves is self-contained. Adding a
+# header here is all a new one needs. SDL_GameControllerDB.h and the generated
+# version.h are installed separately -- neither is an API header.
+set(AKGL_PUBLIC_HEADERS
+  actor
+  assets
+  audio
+  character
+  controller
+  draw
+  error
+  game
+  heap
+  iterator
+  json_helpers
+  physics
+  registry
+  renderer
+  sprite
+  staticstring
+  text
+  tilemap
+  types
+  util
+)
+
 set(GAMECONTROLLERDB_H "include/akgl/SDL_GameControllerDB.h")
 set(prefix      ${CMAKE_INSTALL_PREFIX})
 set(exec_prefix "\${prefix}")
@@ -274,6 +302,30 @@ endforeach()
 
 add_test(NAME semver_unit COMMAND akgl_test_semver_unit)
 
+# One translation unit per public header, each including exactly that header and
+# nothing before it. This is the only shape that proves a header is
+# self-contained: a second #include in the same file proves nothing about the
+# second, because by then the first has dragged its dependencies in. Generated
+# rather than written by hand so the check cannot fall behind
+# AKGL_PUBLIC_HEADERS -- the failure being guarded against is a header nobody
+# remembered to cover.
+set(AKGL_HEADER_SELFTEST_SOURCES "")
+foreach(header IN LISTS AKGL_PUBLIC_HEADERS)
+  set(generated "${CMAKE_CURRENT_BINARY_DIR}/tests/header_${header}.c")
+  file(WRITE "${generated}"
+"/* Generated by CMakeLists.txt from AKGL_PUBLIC_HEADERS. Do not edit. */\n\
+#include <akgl/${header}.h>\n\
+\n\
+/* ISO C forbids an empty translation unit; the compile is the assertion. */\n\
+int akgl_header_selftest_${header}(void);\n\
+int akgl_header_selftest_${header}(void)\n\
+{\n\
+    return 0;\n\
+}\n")
+  list(APPEND AKGL_HEADER_SELFTEST_SOURCES "${generated}")
+endforeach()
+target_sources(akgl_test_headers PRIVATE ${AKGL_HEADER_SELFTEST_SOURCES})
+
 # TIMEOUT is generous because CTest applies the same property to `ctest -T
 # memcheck`, where every suite runs under valgrind at something like twenty
 # times its normal cost. The unit suites finish in well under a second each
@@ -455,24 +507,7 @@ install(FILES ${CMAKE_CURRENT_BINARY_DIR}/akgl.pc DESTINATION "lib/pkgconfig/")
 install(FILES ${CMAKE_CURRENT_BINARY_DIR}/include/akgl/version.h DESTINATION "include/akgl/")
 install(TARGETS akgl DESTINATION "lib/")
 install(FILES "deps/semver/semver.h" DESTINATION "include/")
-install(FILES "include/akgl/actor.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/types.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/text.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/assets.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/audio.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/character.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/error.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/draw.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/game.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/controller.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/heap.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/iterator.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/json_helpers.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/renderer.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/physics.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/registry.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/sprite.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/staticstring.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/tilemap.h" DESTINATION "include/akgl/")
-install(FILES "include/akgl/util.h" DESTINATION "include/akgl/")
+foreach(header IN LISTS AKGL_PUBLIC_HEADERS)
+  install(FILES "include/akgl/${header}.h" DESTINATION "include/akgl/")
+endforeach()
 install(FILES ${GAMECONTROLLERDB_H} DESTINATION "include/akgl/")