fix(compiler): preserve declared type of const references

A const reference lowered to `val(itoa(g.a.ival), "int")` in emit_call.ludic —
the initializer's raw integer bits, hardcoded as `int`. For a fixed const like
`const X: fixed = 10.0` that yielded the Q16.16 bits (655360) typed as int, so
every fixed comparison/arithmetic against it silently broke (it caused an
infinite loop in runtime/native/numeric.ludic, previously worked around with
inline literals).

Fix: a const reference now emits its initializer expression via emit_expr(g.a),
which carries the initializer's real type (E_FLOAT->fixed, E_BOOL->bool,
E_STR->string) and even handles computed initializers. Every existing const is
an int literal, for which this is byte-identical to the old immediate — the
C-free bootstrap fixpoint and all golden renders are unchanged.

- selfhost/tests/const.ludic + sh_case pin fixed/int/bool const behaviour.
- runtime/native/numeric.ludic restored to named fixed consts (HUGE_TEN etc.),
  which the workaround had inlined; the numeric example (20 assertions) still
  passes, validating the fix under runtime splice.

All suites green: x selfhost-test 31/31 (fixpoint holds, goldens byte-identical),
x test 85/85, x test-tools 30/30.

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

selfhost/tests/const.ludic

@@ -0,0 +1,24 @@
+program T {
+  # a const reference carries its initializer's real type — so a `fixed` const
+  # compares and computes as fixed-point, not as its raw i32 bits (the bug this
+  # pins: a fixed const used to lower to an `int` and silently corrupt fixed math).
+  const TEN:   fixed = 10.0
+  const HALF:  fixed = 0.5
+  const LIMIT: int   = 7
+  const STEP:  int   = 3
+  const ON:    bool  = true
+  const OFF:   bool  = false
+  entry {
+    let x: fixed = 10.0
+    if x >= TEN  { print(1) } else { print(0) }   # 1  (equal counts)
+    if x >  TEN  { print(1) } else { print(0) }   # 0  (not strictly greater)
+    print(floor(TEN))                             # 10
+    print(floor(TEN * HALF))                      # 5   (fixed * fixed)
+    print(floor(TEN / HALF))                      # 20  (fixed / fixed)
+    print(floor(x - TEN))                         # 0
+    print(LIMIT + STEP)                           # 10  (int const arithmetic)
+    print(LIMIT)                                  # 7
+    if ON  { print(1) } else { print(0) }         # 1  (bool const true)
+    if OFF { print(1) } else { print(0) }         # 0  (bool const false)
+  }
+}