feat(senses): walkers slide round still things, and lines of sight are the world's to answer

- ludic.wildlife: WildlifeWorld.push / pushed_x / pushed_z (defaults change nothing); a ground
  walker's step is slid clear of a still thing with a body from its species' size and scale, and
  a step that gets nowhere turns away as the water does. Birds are not pushed; no dice added.
- ludic.npc: NpcWorld.push / pushed_x / pushed_z (a person 0.35 m round) in npc_walk, and
  NpcWorld.clear (default true), which npc_line_ok asks at 1 m so a detour does not cut a trunk.
- ludic.aim: AimView.clear replaces AimView.ground and the ground march; the pick asks the line
  a body's width short of where the ray enters the thing (aim_clear_at(t, back)), so a solid
  thing does not hide itself. probe.ludic (the ground-agreement probe) and AimView.dry are gone.
- ludic.photo: PhotoLens.clear replaces PhotoLens.ground, PhotoLens.trunk and the march.

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

packages/ludic.npc/ground.ludic

@@ -1,5 +1,5 @@
 # ground.ludic - where a person can stand and walk: dry, gentle, allowed; a straight walk with no
-# water and no scramble on it; a spot in a ring, a spot toward something, and the nearest shore.
+# water, scramble or still thing on it; a spot in a ring, a spot toward something, the nearest shore.
 # A finder that succeeds leaves its answer in npc_px / npc_pz (and the water in npc_wx / npc_wz).
 
 export function npc_px(npc_st: NpcState) -> float { return npc_st.np_px }
@@ -18,6 +18,7 @@ export function npc_line_ok(ax: float, az: float, bx: float, bz: float) -> bool
   var n = int(d / 1.5)
   if n < 1 { n = 1 }
   var prev = NpcWorld.ground(ax, az)
+  if not NpcWorld.clear(ax, prev + 1.0, az, bx, NpcWorld.ground(bx, bz) + 1.0, bz) { return false }   # a trunk, a tent
   for i in 1 .. n + 1 {
     let t = float(i) / float(n)
     let x = ax + (bx - ax) * t