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/README.md

@@ -78,6 +78,8 @@ a `fill` line's words are `NpcTalk.say(p, line)`, and "" means it has nothing tr
 export port NpcWorld {       # every member has a default: a flat dry field at noon, one player, nobody wanted
   ground, water, slope: fn(float, float) -> float
   allowed: fn(float, float) -> bool                  # may a person stop here
+  push: fn(x, z, r, feet, head) -> bool, pushed_x, pushed_z   # a walker slid clear of still things (r 0.35)
+  clear: fn(ax, ay, az, bx, by, bz) -> bool          # no still thing between: npc_line_ok asks it at 1 m
   hour: fn() -> float, day: fn() -> int              # the clock
   players: fn() -> int, player_on: fn(int) -> bool, player_x / player_z: fn(int) -> float
   want: fn() -> int, extra: fn() -> int              # the census: how many, and a kind brought out regardless (-1)