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/mir/optimizer_passes/normalize.rs

@@ -1,6 +1,6 @@
 use crate::mir::optimizer::MirOptimizer;
 use crate::mir::optimizer_stats::OptimizationStats;
-use crate::mir::{BarrierOp, MirInstruction, MirModule, TypeOpKind, ValueId, WeakRefOp};
+use crate::mir::{BarrierOp, MirModule, TypeOpKind, ValueId, WeakRefOp};
 
 pub fn force_plugin_invoke(_opt: &mut MirOptimizer, module: &mut MirModule) -> OptimizationStats {
     use crate::mir::MirInstruction as I;