fix: resolve all GitHub CodeQL security/quality alerts

Fix 9 integer-multiplication-cast-to-long warnings across 6 files:
- wmo_renderer.cpp: grid cell count and height variance calculation
- composite_renderer.cpp: overlay tile grid allocation
- vk_texture.cpp: image size calculation (width*height*bpp)
- m2_renderer.cpp: collision grid cell allocation
- character_renderer.cpp: normal map buffer and height variance
- world_entry_callback_handler.cpp: tile reserve count

All fixes cast operands to size_t/double before multiplication to
prevent integer overflow when dimensions are large.

src/rendering/world_map/composite_renderer.cpp

@@ -30,7 +30,7 @@ void CompositeRenderer::ensureTextureSlots(size_t zoneCount, const std::vector<Z
             slots.overlays.resize(zones[i].overlays.size());
             for (size_t oi = 0; oi < zones[i].overlays.size(); oi++) {
                 const auto& ov = zones[i].overlays[oi];
-                slots.overlays[oi].tiles.resize(ov.tileCols * ov.tileRows, nullptr);
+                slots.overlays[oi].tiles.resize(static_cast<size_t>(ov.tileCols) * static_cast<size_t>(ov.tileRows), nullptr);
             }
         }
     }