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.

README.md

@@ -18,7 +18,7 @@ Ghidra.
 
 ## Status
 
-OpenRA3 is at **v0.7.0**. The engine compiles and runs headless, and a **minimal
+OpenRA3 is at **v0.8.0**. The engine compiles and runs headless, and a **minimal
 skirmish** is playable: it reads a real multiplayer map out of your install,
 recovers the player start waypoints, and simulates two sides building a base,
 extracting ore and fighting until one side is wiped out. The balance is the
@@ -307,9 +307,10 @@ path rasterises it with a z-buffer. Match state is
 overlaid (start markers in yellow, player 0 in blue, player 1 in red).
 `--thumbnail` uses the old `<map>_art.tga` overview instead.
 
-> **Not yet drawn:** the map's `Road` objects (the sidewalk/road segments that
-> reference a `Road` template rather than a mesh) need the retail road-network
-> mesher and are skipped; they are reported in the `objects: … missing` count.
+> **Roads / sidewalks** are drawn too: the map stores each as a
+> `RoadType::Start`/`End` pair of objects, and `render` emits a flat textured
+> ribbon along each segment, lifted onto the terrain with a small depth bias so
+> it does not clip into the ground.
 
 **Offscreen image** (works anywhere, no display needed):