Patrols everywhere they should be, and concrete that has to be poured

Three fixes, all from watching it run.

Cars stuck against buildings. routeTo dropped the node a route starts from,
which is fine for a unit standing on it and wrong for anything re-routing from
mid-segment: its first leg became a straight line to a node two hops away,
across buildings and open country. Routes now include their start node so a unit
rejoins the road before setting off.

No patrols anywhere. They only existed as a reaction to the player's own tracks,
so hostile territory was empty until you had personally made a road notorious.
Enemy ground now carries standing patrols by how dangerous it is — none behind
your lines, five on the frontier — spawned onto their roads so the territory has
them the moment you arrive.

This surfaced a second bug: dispatched units were culled at 546m from the player
while dispatch origins reached 600m, so a patrol or engineer could be deleted on
its first step and simply never turn up. Anything with an assignment is now kept
regardless of range; its expiry still bounds it.

Barricades appearing instantly. Crossing a heat threshold placed concrete on the
road with nobody involved. Construction is now staged: an engineer is dispatched
for the barricade, another for the tower, and heatProps is driven by finished
builds rather than by heat levels. It still refuses to close a slab around a car
parked in the gap.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/render/units.ts

@@ -122,7 +122,10 @@ export function createUnitView(scene: THREE.Scene) {
       let towerCount = 0;
       for (const site of units.checkpoints.values()) {
         if (towerCount >= towers.count) break;
-        const built = site.built;
+        // A tower only stands once its own stage is done. While the barricade
+        // is going up there is nothing here but activity.
+        const built = site.done.includes('tower');
+        if (!built && site.stage !== 'tower') continue;
         const height = built ? 1 : Math.max(0.15, site.progress);
         position.set(site.x, (6 * height) / 2, site.z);
         scratch.compose(position, quaternion.identity(), scale.set(1, height, 1));