vm/router: minimal special-method extension (equals/1); toString mapping kept

mir: add TypeCertainty to Callee::Method (diagnostic only); plumb through builder/JSON/printer; backends ignore behaviorally

using: confirm unified prelude resolver entry for all runner modes

docs: update Callee architecture with certainty; update call-instructions; CURRENT_TASK note

tests: quick 40/40 PASS; integration (LLVM) 17/17 PASS

src/backend/mir_interpreter/mod.rs

@@ -20,6 +20,7 @@ pub(super) use crate::mir::{
 mod exec;
 mod handlers;
 mod helpers;
+mod method_router;
 
 pub struct MirInterpreter {
     pub(super) regs: HashMap<ValueId, VMValue>,