Bump libtcod-headless to 79abc66 (FOV overflow fixes); closes #321

#321 was an ASan heap-buffer-overflow in view_array_insert
(fov_permissive2.c:97) reached via ColorLayer.draw_fov ->
GridData::computeFOV -> TCOD_map_compute_fov_permissive2, surfaced by the
#312 fuzz_fov campaign. The "bad-free in ~GridData" in the issue title is
the downstream symptom of this active_views buffer overflow.

The bump pulls in four upstream FOV commits:
  - off-by-one in view_array_insert overflowing active_views  <- root cause
  - undersized bumps buffer overflow on tiny permissive maps
  - MRPAS obstacle buffer overflow / malloc(0) on small maps
  - regression tests for FOV

Verified by A/B replay of the fuzz_fov crash corpus under clang-18 ASan,
same build config (clang-18, -DLIBTCOD_SDL3=OFF, identical sanitizer
flags) with only the submodule commit differing:
  pre-fix  (8835239): fov-crash-5f34f68e and fov-crash-a451db54 abort with
                      heap-buffer-overflow in view_array_insert inside
                      GridData::computeFOV
  post-fix (79abc66): all crash inputs clean; 45s / 21,952-run fov fuzz
                      smoke clean, no new crashes

Note: __lib/libtcod.so (gitignored, the shipped desktop lib) must be
rebuilt from this submodule commit for release binaries to carry the fix.

Also updates ROADMAP: #321 moved to Recently Shipped; open-issue count
refreshed to the post-#312 tracker state.

closes #321

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TvvE6TB2cScBVbeap2btHw

modules/libtcod-headless

@@ -1 +1 @@
-Subproject commit 8835239f8b8170a35027b2d4f19edd7c08ba9218
+Subproject commit 79abc66578fc757c57e561106f9e26d21f42f5e0