DevTools debugger: evaluate expressions at the breakpoint

The debugger's paused state stops being read-only. When execution is paused - at a `debugger;` statement or a thrown exception - the Console now evaluates whatever you type in the PAUSED FRAME's scope, not the page's: type `secret * 2` at a breakpoint and it reads the `secret` that was in scope at the pause, with inner block variables correctly shadowing outer ones. It is the standard Debugger.evaluateOnCallFrame, wired so the existing Console REPL just does the right thing: paused -> evaluate in the frame, running -> evaluate in the live page, exactly like the reference browser. The frame's variables are captured at the pause and offered to the expression as a scope, so an expression can read and combine them even after the throw has unwound. DevTools moves 25 to 26; overall holds at 51.