feat(lang): float and double types with ordinary operators

`float` (32-bit) and `double` (64-bit) with + - * / %, comparisons and unary minus.
Decimal literals take their type from context and stay `fixed` elsewhere; int and long
promote implicitly (LUDIC_WARN_FLOAT_PROMOTE=1 lists every promotion). float(), double(),
int(), long() and fixed() convert; floats(n)/doubles(n) buffers; float fields, globals,
constants and parameters; Math.* computes in float for float arguments; string/print
write the shortest round-tripping decimal; float_bits/float_from_bits expose the bits.
@deterministic code may not use floats. The f_* runtime helpers stay as they are.

Editors know the new type words; the JetBrains plugin is 1.5.0.

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

selfhost/backend/game/emit_game.ludic

@@ -4,6 +4,7 @@
 # called only when the runtime defines them.
 
 function emit_system_fn(sys: Node) -> void {
+  det_enter(sys.s)
   g_cur_scene = sys.c                          # scene owning this handler (null if global) — for `become`
   ll_t = 0;  ll_lbl = 0;  g_term = false;  loc_reset();  nloop = 0;  nself = 0
   ret_ty = "void"
@@ -19,6 +20,7 @@ function emit_system_fn(sys: Node) -> void {
   emit(buf_str(falloc))
   emit(buf_str(fbody))
   emit("}\n\n")
+  g_det_ctx = ""
 }
 
 # one enable-gated call to @sys_<d.s> (skipped while the handler is disabled).