Fix the two Doxygen errors that were failing the docs build

`Doxyfile` sets `WARN_AS_ERROR = FAIL_ON_WARNINGS` and CI builds the docs as a
step of `cmake_build`, so both of these failed the job:

- `akgl_character_initialize` documented `@param basechar` for a parameter the
  declaration spells `obj`. This is exactly the mismatch AGENTS.md warns about
  under Naming Conventions -- "parameter names must match between the
  declaration and the definition, Doxygen publishes the header spelling" -- and
  it cost two errors, one for the argument that does not exist and one for the
  argument left undocumented.
- `require_at_eof` asked for an explicit link to `#AKERR_EOF`. That symbol is
  libakerror's and `Doxyfile`'s INPUT is `include/akgl src`, so the link can
  never resolve. Backticks say the same thing to a reader without asking
  Doxygen to find a page it does not have.

`doxygen Doxyfile` now exits 0 with no diagnostics.

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

include/akgl/character.h

@@ -47,7 +47,7 @@ typedef struct akgl_Character {
  * reference. Everything numeric (speeds, accelerations, `speedtime`) is left at
  * zero for the caller -- or akgl_character_load_json -- to fill in.
  *
- * @param basechar Pooled character to initialize, normally straight from
+ * @param obj Pooled character to initialize, normally straight from
  *                 akgl_heap_next_character. Required. Any previous contents are
  *                 discarded without releasing the sprites they referenced.
  * @param name     Registry key, NUL-terminated. Required. Truncated at