bridge/json_v0: split expr lowering; add Ternary/Peek lowering + AST; selfhost Peek JSON emit; add selfhost Peek smoke; warning cleanup in lowering/optimizer/verification

- Split expr lowering into ; route calls from stmt lowering
- Implement ternary/peek lowering (MIR13 PHI-off=Copy, PHI-on=Phi)
- Extend JSON v0 AST (ExprV0::{Ternary,Peek}, PeekArmV0)
- Selfhost parser_box: emit Peek JSON; add Stage-2 'Peek basic' smoke
- Reduce warnings: remove unused imports/vars in several modules
- current_task: update plan for legacy VM/Interpreter offboarding

src/parser/expressions.rs

@@ -7,7 +7,7 @@
 
 use super::common::ParserUtils;
 use super::{NyashParser, ParseError};
-use crate::ast::{ASTNode, BinaryOperator, LiteralValue, Span, UnaryOperator};
+use crate::ast::{ASTNode, Span, UnaryOperator};
 use crate::tokenizer::TokenType;
 
 // Debug macros are now imported from the parent module via #[macro_export]