Add Source/accessibility/ with four new modules:
- speech.cpp/hpp: low-HP warnings, durability warnings, boss/monster
HP announcements, interactable door announcements
- tracker.cpp/hpp: TrackerTargetCategory, path-finding predicates,
tracker navigation (cycle, navigate, auto-walk)
- town_navigation.cpp/hpp: town NPC selection, listing, auto-walk
- location_speech.cpp/hpp: BFS path-finding for speech, player status
announcements, nearest-exit/stairs/portal speech, keyboard walk
Wire the new modules into diablo.cpp via four include lines.
Declare CanPlayerTakeAction() and CancelAutoWalk() in diablo.h.
Add the four new source files to Source/CMakeLists.txt.