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-int.md

@@ -0,0 +1,25 @@
+---
+id: fn-int
+name: int
+category: builtins
+kind: builtin
+tokens: int long
+sig: int(x) -> int / long(x) -> long
+tip: Convert a number to a whole number, truncating toward zero.
+order: 52
+---
+
+Converts a <code>float</code>, <code>double</code>, <code>fixed</code> or <code>long</code> to an <code>int</code> (or, with <code>long(x)</code>, to a <code>long</code>). Floating-point values truncate toward zero, as in C: `int(2.9)` is <code>2</code> and `int(-2.9)` is <code>-2</code>. A <code>fixed</code> value rounds down, like <code>floor</code>. For other rounding use <code>Math.floor</code>, <code>Math.ceil</code> or <code>Math.round</code>.
+
+Parameters:
+- `x` — the number to convert
+
+```ludic
+program Whole {
+  entry {
+    let pixels: float = 12.75
+    print(int(pixels))                 # 12
+    print(long(pixels * 1000.0))       # 12750
+  }
+}
+```