Introduce `GameServices` struct — an explicit dependency bundle that
`Application` populates and passes to `GameHandler` at construction time.
Eliminates all 47 hidden `Application::getInstance()` calls in
`src/game/*.cpp`, completing SOLID-D (dependency-inversion) cleanup.
Changes:
- New `include/game/game_services.hpp` — `struct GameServices` carrying
pointers to `Renderer`, `AssetManager`, `ExpansionRegistry`, and two
taxi-mount display IDs
- `GameHandler(GameServices&)` replaces default constructor; exposes
`services() const` accessor for domain handlers
- `Application` holds `game::GameServices gameServices_`; populates it
after all subsystems are created, then constructs `GameHandler`
(fixes latent init-order bug: `GameHandler` was previously created
before `AssetManager` / `ExpansionRegistry`)
- `game_handler.cpp`: duplicate `isActiveExpansion` / `isClassicLikeExpansion` /
`isPreWotlk` anonymous-namespace helpers removed; `game_utils.hpp`
included instead
- All domain handlers (`InventoryHandler`, `SpellHandler`, `MovementHandler`,
`CombatHandler`, `QuestHandler`, `SocialHandler`, `WardenHandler`) replace
`Application::getInstance().getXxx()` with `owner_.services().xxx`
