v0.8.0: map roads/sidewalks, per-vertex depth bias, retail camera controls

- ra3.map: capture the object RoadType; ra3.models pairs the map's
  Start/End road objects and drapes a flat textured ribbon along each
  segment (tessellated to the relief).
- Ground decals (roads/sidewalks) get a per-vertex screen-space depth
  offset (scene::vertex.bias) applied in the object shader and the
  software rasteriser, so they no longer z-fight or clip into the
  terrain at top-down angles.
- Tactical view aligned with retail (SAGE LookAtTranslator): middle-drag
  orbits yaw/pitch, a middle click resets angle/pitch/zoom, arrow keys
  pan, wheel zooms within the retail zoom range; WASD pan removed and
  left-drag no longer rotates.
- ui_event gains middle/right/released buttons; Vulkan + SDL map them.
- docs: roads, depth bias and camera controls.

apps/openra3/main.cpp

@@ -255,7 +255,7 @@ namespace {
             const auto stream = ra3::models::asset_stream::load_files(paths->manifest, paths->bin);
             std::vector<ra3::models::placement> placements;
             for (const auto &object: ra3::map::parse_objects(ckmp)) {
-                placements.push_back({object.type, object.x, object.y, object.z, object.angle, object.scale});
+                placements.push_back({object.type, object.x, object.y, object.z, object.angle, object.scale, object.road_type});
             }
             const auto world_w = terrain.world_width();
             const auto world_h = terrain.world_height();
@@ -265,8 +265,8 @@ namespace {
                 const auto cy = std::min(terrain.height - 1U, static_cast<ra3::core::uint32>((world_h - y) / ra3::terrain::cell_size));
                 return static_cast<float>(terrain.elevation(cx, cy)) * options.z_scale;
             });
-            std::printf("objects: %zu placed, %zu missing, %zu triangles, %zu textures (%s)\n", scene.placed, scene.missing, scene.triangle_count(),
-                        scene.textures.size(), paths->bin.filename().string().c_str());
+            std::printf("objects: %zu placed, %zu missing, %zu road segments, %zu triangles, %zu textures (%s)\n", scene.placed, scene.missing,
+                        scene.roads, scene.triangle_count(), scene.textures.size(), paths->bin.filename().string().c_str());
         } catch (const std::exception &error) {
             std::printf("objects: failed to build scene (%s)\n", error.what());
         }