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.

src/render/ra3.render.cppm

@@ -277,6 +277,9 @@ export namespace ra3::render {
         float dy = 0.0F;
         float wheel = 0.0F;
         bool left = false;
+        bool middle = false;
+        bool right = false;
+        bool released = false; ///< mouse_button: true for a button-up event.
     };
 
     /** A warm red/gold loading screen with a progress bar (0..1). */
@@ -675,7 +678,9 @@ export namespace ra3::render {
         float pitch = 1.02F;   ///< Radians above the horizon (~58 degrees down).
         float height = 420.0F; ///< Camera height above the target's ground.
         float fov = 0.85F;     ///< Vertical field of view, radians.
-        float min_height = 120.0F;
-        float max_height = 1600.0F;
+        // Zoom range mirrors the retail TacticalView (zoom 0.2..1.3 around the
+        // default height): closer/farther than that is clamped.
+        float min_height = 320.0F;
+        float max_height = 2100.0F;
     };
 }