Function check_program 

pub fn check_program(
    stmts: &[Stmt<'_>],
    interner: &Interner,
    registry: &TypeRegistry,
) -> Result<TypeEnv, TypeError>

Check a LOGOS program and return a typed TypeEnv for codegen.

Replaces TypeEnv::infer_program. Returns Err(TypeError) only on genuine type contradictions (e.g., Let x: Int be "hello"). Ambiguous types fall back to LogosType::Unknown silently.