Final missions above ground (M30, co-op M20), surface option for versus matches, docs

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/ROADMAP.md

@@ -30,7 +30,7 @@ Stone bridges over lava exist already (75 gold per tile).
 Built as: `src/bridges.rs` (fire, wear, drawbridges, obsidian), the *Drawbridge* tool (click: down → up →
 automatic) and the *Frost* spell (lava → obsidian for 40 s); the frost glow trap keeps lava next to it cooled.
 
-## 3. The surface world
+## 3. The surface world – done (v202611-00038)
 
 1. **Surface terrain** – grass, trees, paths, daylight and sky. Trees act like earth: imps fell
    them.
@@ -48,6 +48,18 @@ automatic) and the *Frost* spell (lava → obsidian for 40 s); the frost glow tr
    with the High Marshal's fortress to destroy. Free play and multiplayer get a map option
    "Surface". The map editor gets the new terrain.
 
+Built as: `src/wood.rs` (wood, giant mushrooms), `src/walls.rs` (the wall tool), `src/surface.rs` (sky layer
+`Map::sky`, forests, cliffs and cave mouths, clearings around fortresses), `src/siege.rs` (rams and catapults:
+in hero waves from wave 4/6, buildable with a forge). The fortresses above ground are the knights' usual
+fortresses (fortress.rs) in a clearing. Final missions: campaign M30 and co-op M20; free play, versus matches
+and editor random maps have the option "half above ground".
+
+## 3b. Music (next milestone)
+
+Six more underground tracks and a block of six surface tracks: the same leitmotif brighter and in major, synthetic
+birdsong and wind, flute leads and harp arpeggios. The music follows the camera (surface or underground) with a
+crossfade.
+
 ## 4. Additions
 
 1. **Random events** – earthquake (tunnels cave in), lava eruption, flood, gold vein found. Rare