Reindent all C sources to the canonical stroustrup style

Mechanical whitespace-only change across src/, include/, tests/, and
util/, applied with scripts/reindent.sh. No behavioral change.

Most files already conformed. The genuine outliers indented at 2 columns
(json_helpers.c, util.c from akgl_rectangle_points onward, assets.c,
staticstring.c, akgl_actor_add_child, util.h, staticstring.h) or used
spaces where the canonical form is a tab (draw.c). cc-mode also re-aligns
line-continuation backslashes in multi-line macros to its default
c-backslash-column, which is required for the tree to be a fixed point of
the indenter.

Verified whitespace-only: `git diff -w` over this change is empty apart
from three trailing blank lines removed at EOF in src/heap.c,
src/registry.c, and tests/tilemap.c. The build produces no new errors and
ctest is unchanged at 13/14, with `character` still the one intentional
failure.

The tree is now a fixed point of `scripts/reindent.sh --check`.

include/akgl/SDL_GameControllerDB.h is generated and excluded.

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

include/akgl/physics.h

@@ -26,7 +26,7 @@ typedef struct akgl_PhysicsBackend {
     double gravity_y;
     double gravity_z;
     SDL_Time gravity_time;
-    SDL_Time timer_gravity;    
+    SDL_Time timer_gravity;
 } akgl_PhysicsBackend;
 
 /**