fence: every runtime call is its line's site, and site 0 comes back when it returns

A block took whatever @lp_site held when it was made. Only malloc, calloc, realloc, concat, the number
texts, the float text, a substring and Text.* set one, so every other runtime helper - intern,
Text.repeat and the string builders, the Fs, Os, unicode, uuid and crypto helpers - was charged to
whichever line had allocated last (walk 9 blamed gvk_tex_storage, m4_new, kept_push$int and
survey_op_reward for intern's 16 B copies).

- Any `call ptr @lp_*` now takes a site of its own, its kind the callee's name when no better one is
  known (intern, str_repeat, fs_list, ...). What the helper makes, in however many blocks and
  through whichever helpers it calls in turn, is that line's.
- When the call returns, @lp_site goes back to site 0, now named "(runtime) (no site) unsited": a
  block made with no site of its own says so instead of borrowing the last one.
- The ECS stores' grows and a mod's registered stores - the only allocations emitted outside
  emit_bind - take a site each.

Golden alloc_fence_sites: two lines take turns keeping memory, Text.repeat and a record, every frame
judged. Each report names its own line (25 x +32 B str_repeat at :11, 25 x +16 B new Box at :12);
the toolchain before this charges 23 of the 32 B texts to the new Box line. The other fence and arena
goldens are unchanged; ludic.base's tests pass; the game's frame ratchets are 0 on main 7cb2b164.

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

selfhost/backend/emit_intrin.ludic

@@ -22,6 +22,7 @@ function emit_bind(rest: pointer) -> pointer {
   let r = nreg()
   emit("  ");  emit(r);  emit(" = ");  emit(rest);  emit("\n")
   if want { emit("  store i8 0, ptr @lp_want\n") }
+  if g_site_reset { emit("  store i32 0, ptr @lp_site\n");  g_site_reset = false }
   return r
 }