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>

docs/language/builtins/fn-float_bits.md

@@ -0,0 +1,24 @@
+---
+id: fn-float_bits
+name: float_bits
+category: builtins
+kind: builtin
+tokens: float_bits float_from_bits double_bits double_from_bits
+sig: float_bits(x) -> int / float_from_bits(bits) -> float
+tip: A float's IEEE bit pattern as an int, and back.
+order: 53
+---
+
+<code>float_bits(x)</code> returns the 32 bits of a <code>float</code> as an <code>int</code>, and <code>float_from_bits(bits)</code> reads them back. <code>double_bits</code> / <code>double_from_bits</code> do the same for a <code>double</code> with a <code>long</code>. Use them where a float has to travel as raw data: a file format, a network packet, or a <code>words</code> buffer shared with code that still stores bit patterns.
+
+Parameters:
+- `x` — the float to encode (`float_bits`), or the bits to decode (`float_from_bits`)
+
+```ludic
+program Bits {
+  entry {
+    print(float_bits(1.0))             # 1065353216 (0x3F800000)
+    print(float_from_bits(0x40000000)) # 2.0
+  }
+}
+```