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>

tools/x/selfhost_test.ludic

@@ -87,6 +87,7 @@ function cmd_selfhost_test() -> int {
   sh_case("control", "55 4 15 1")
   sh_case("match_bits", "1 2 9 16 4 15")
   sh_case("fixed", "2 3 0 6 1")
+  sh_case("const", "1 0 10 5 20 0 10 7 1 0")
   sh_case("math", "3 7 5 10 -1 0 1 2 3 3 2 5 25 50")
   sh_case("math2", "1414 3 999 999 499 5 5 25 3142 179 4 2 7 25 30 500")
   sh_case("textlist", "3 10 30 1 0 2 -1 30 10 10 30 30 2 0 11 104 1 0 1 0 1 0 6 -1 42 5 1 4 4")