refactor(lang): rename builtins flr->floor and fx->fixed

De-abbreviate the two bare fixed-point conversion builtins:
  flr(f) -> int     ->  floor(f) -> int    (fixed -> int, flooring)
  fx(i)  -> fixed   ->  fixed(i) -> fixed  (int -> fixed; mirrors how the
                                            stringify builtin is `string`)

Updates the compiler dispatch, all call sites, the grammars/LSP/JetBrains
tokens, and the docs (fn-flr -> fn-floor, fn-fx -> fn-fixed). Reseeded;
C-free fixpoint holds; all suites green (45/24/29); site + check.py OK.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/language/builtins/fn-fixed.md

@@ -1,15 +1,15 @@
 ---
-id: fn-fx
-name: fx
+id: fn-fixed
+name: fixed
 category: builtins
 kind: builtin
-tokens: fx
-sig: fx(n) -> fixed
+tokens: fixed
+sig: fixed(n) -> fixed
 tip: Lift an integer into a Q16.16 fixed-point value.
 order: 50
 ---
 
-Converts an integer into a <code>fixed</code> value (Ludic's Q16.16 fixed-point type), so it can take part in fractional arithmetic. Ludic has no floating point; <code>fixed</code> is how you carry sub-pixel precision for smooth movement and physics-like accumulation. Use <code>fx</code> when you need to combine an <code>int</code> with fixed-point values or divide to get a fraction — for example <code>fx(1) / fx(4)</code> is <code>0.25</code>. Convert back to a whole number for drawing with <code>flr</code>.
+Converts an integer into a <code>fixed</code> value (Ludic's Q16.16 fixed-point type), so it can take part in fractional arithmetic. Ludic has no floating point; <code>fixed</code> is how you carry sub-pixel precision for smooth movement and physics-like accumulation. Use <code>fixed</code> when you need to combine an <code>int</code> with fixed-point values or divide to get a fraction — for example <code>fixed(1) / fixed(4)</code> is <code>0.25</code>. Convert back to a whole number for drawing with <code>flr</code>.
 
 Parameters:
 - `n` — the integer to lift into fixed-point
@@ -17,10 +17,10 @@ Parameters:
 ```ludic
 program SmoothAccumulate {
   handler ComputeStep phase Start {
-    let full_speed = fx(3)
-    let half_speed = full_speed / fx(2)
+    let full_speed = fixed(3)
+    let half_speed = full_speed / fixed(2)
     let two_steps = half_speed + half_speed
-    print(flr(two_steps))
+    print(floor(two_steps))
   }
 }
 ```

docs/language/builtins/fn-floor.md

@@ -1,15 +1,15 @@
 ---
-id: fn-flr
-name: flr
+id: fn-floor
+name: floor
 category: builtins
 kind: builtin
-tokens: flr
-sig: flr(x) -> int
+tokens: floor
+sig: floor(x) -> int
 tip: Floor a fixed-point value down to the nearest integer.
 order: 50
 ---
 
-Converts a <code>fixed</code> (Q16.16) value back to an <code>int</code> by discarding the fractional part, rounding toward negative infinity. It is the counterpart to <code>fx</code>: you accumulate motion in fixed-point for sub-pixel smoothness, then <code>flr</code> the result to get the whole-pixel column or row to draw at. Because it floors rather than rounds, <code>flr(fx(3) / fx(2))</code> is <code>1</code>, not <code>2</code>. Use it wherever a fixed value must become an integer coordinate, count, or index.
+Converts a <code>fixed</code> (Q16.16) value back to an <code>int</code> by discarding the fractional part, rounding toward negative infinity. It is the counterpart to <code>fx</code>: you accumulate motion in fixed-point for sub-pixel smoothness, then <code>floor</code> the result to get the whole-pixel column or row to draw at. Because it floors rather than rounds, <code>floor(fixed(3) / fixed(2))</code> is <code>1</code>, not <code>2</code>. Use it wherever a fixed value must become an integer coordinate, count, or index.
 
 Parameters:
 - `x` — the fixed-point value to floor
@@ -20,8 +20,8 @@ program FixedToPixels {
 
   handler DrawWorld phase Render {
     Screen.clear(Color.MidnightBlue)
-    let smooth_column = fx(5) + fx(1) / fx(2)
-    let pixel_x = flr(smooth_column) * TILE_SIZE
+    let smooth_column = fixed(5) + fixed(1) / fixed(2)
+    let pixel_x = floor(smooth_column) * TILE_SIZE
     Screen.fill_rectangle(x: pixel_x, y: 32, width: TILE_SIZE, height: TILE_SIZE, color: Color.LimeGreen)
     Screen.show()
   }