t27b: an untyped var set to an integer literal takes the reference's u32/u64 width; an untyped undefined const is accepted (StmtLocal) #6967

Refs #6063 (coverage lane 1, family StmtLocal, rank 4 in tri t27b next on lab run 62e27a1; ranks 1-3 are lane 2's #6866 / #6961 and lane 1's #6965)

Problem

t27b refuses two shapes of untyped local that the reference compiles and runs:

1. var i = 0; is refused as "var i initialised with an untyped integer needs a type". The reference's gen-zig (zig_int_literal_default_type in bootstrap/src/compiler.rs) pins the width: var i: u32 = 0;. It uses u64 when the literal does not fit u32, and a literal suffix wins. This applies only when the initializer is a bare integer literal. var x = -1, var x = 0.0 and var n = N stay untyped, and Zig refuses them.
2. const _config = undefined; is refused as "_config has neither type nor value". The reference prints it as it is, plus _ = _config; when nothing reads it, and Zig accepts it.

These shapes alone block two files that the reference passes:

• specs/port/trinity/src/brain/orbitofrontal_value.t27 (4 reference tests)
• specs/port/trios/crates/trios-cli/src/cmd/submit.t27 (4 reference tests)

Spec first

specs/tri/t27b/conformance/untyped_local.t27 gives 6 tests: 6 pass under t27c test-report on the lab, with 13 runtime asserts and 0 vacuous. Wrapping arithmetic (0 -% 1 == 4294967295) makes the u32 / u64 choice observable.

Plan

In cli/t27b/src/lower.rs local_with:

• An untyped var whose initializer is a bare integer literal takes the reference's width, as if it had been declared with that type.
• An untyped const set to undefined binds nothing, so a read of it is still refused.

Everything else stays refused as StmtLocal.

Owner approval

The owner put the label owner-approved-foreign on epic #6063 ("add the label yourself and do the work", translated). The Rust edit is minimal and is listed in tools/policy/foreign-exceptions.txt.