Completes issue 0095: a non-integral float→int narrowing via a FLOAT-const
leaf (`F : f64 : 2.5; y : s64 = F + 0.25` = 2.75) silently truncated to 2.
`evalConstFloatExpr` delegated only INTEGER leaves to `evalConstIntExpr` and
had no float-const leaf arm, so the unified rule never saw the value.
- program_index.zig: add `moduleConstFloat`/`moduleConstFloatFramed` — the f64
twin of `moduleConstInt` (same `isCountableConstType` gate, same cyclic-
definition frame), recovering a numeric module const's value via
`evalConstFloatExpr`. Add `lookupFloatName` to `ModuleConstCtx` and the
`.identifier`/`.type_expr` leaf arms to `evalConstFloatExpr` that call it.
Integer / integral-float leaves keep resolving through the existing
`evalConstIntExpr` delegation, so the unified rule now applies to ANY
compile-time-constant float expression — literal, int-const leaf, float-const
leaf, and combinations — at every binding site.
- lower.zig: add `Lowering.lookupFloatName` delegating to `moduleConstFloat`.
Route `typedConstInitFits`' integral-fold check through `evalConstFloatExpr` +
`floatToIntExact` (the SAME facility `foldComptimeFloatInit` uses) instead of
the int-only `evalComptimeInt`, which folded leaf-by-leaf in i64 and so
rejected an integral SUM built from a non-integral float leaf
(`K : s64 : F + 1.5` = 4.0 now folds; `K : s64 : F + 0.25` errors).
A LOCAL `::` const leaf is a scope ref (not in the const tables) so neither
the int nor float evaluator folds it — float now matches int exactly there.
Regression: examples/1146 (negative) + 0168 (positive) extended with
float-const-leaf cases at local/field/param/const; unit test in
program_index.test.zig covers the leaf resolution (F→2.5, F+0.25→2.75,
F+1.5→4.0). specs.md + readme.md state the rule covers any compile-time-const
float expression incl. float-typed const leaves. issues/0095 banner updated.
Gate: zig build + zig build test green; 447 examples pass, 0 failed.
b6d66d9c56