fix(0113): negated-literal global initializers fold as constants

globalInitValue had no unary_op arm, so g : s64 = -1; fell into the
catch-all 'must be initialized by a compile-time constant' even though
constExprValue already folds negate(literal) for the module-const
identifier route. The new arm routes through constExprValue and applies
the direct-literal rules to the folded value: checkIntLiteralFits on
ints (g : s8 = -300 gets the range diagnostic), and a negated float at
an integer global narrows only when integral (-4.0 folds to -4, -4.5
errors). Binary-op initializers keep the specific non-constant
diagnostic.

Regression: examples/0175-types-negative-literal-global.sx.

issues/0113-negative-literal-global-initializer-rejected.md

@@ -1,3 +1,24 @@
+# RESOLVED — 0113: negative-literal global initializer rejected as "not a compile-time constant"
+
+**Root cause:** `globalInitValue` (src/ir/lower/decl.zig) had no `.unary_op`
+arm, so a negated literal fell into the catch-all "must be initialized by a
+compile-time constant" — even though `constExprValue` already folds
+`negate(int/float literal)` for the module-const identifier route.
+
+**Fix:** a `.unary_op` arm routes the initializer through `constExprValue`;
+the folded value follows the direct-literal rules — `checkIntLiteralFits` on
+ints (`g : s8 = -300;` gets the range diagnostic, not "non-constant"), and a
+negated float at an integer global narrows only when integral
+(`g : s64 = -4.0;` → -4; `-4.5` errors). Binary-op initializers
+(`g : s32 = 2 + 3;`) remain unsupported and keep the specific
+"must be initialized by a compile-time constant" diagnostic — const-expr
+folding for those is a separate feature if ever wanted.
+
+**Regression test:** `examples/0175-types-negative-literal-global.sx`
+(prints `-1 -4 -128`; failed "non-constant" pre-fix).
+
+---
+
 # 0113 — negative-literal global initializer rejected as "not a compile-time constant"
 
 **Symptom.** A top-level global initialized with a negated literal fails to

issues/0113-negative-literal-global-initializer-rejected.sx

@@ -1,4 +0,0 @@
-#import "modules/std.sx";
-g : s64 = -1;
-main :: () { print("{}
-", g); }