DevTools breakpoints snap to the nearest real line

A robustness fix that finishes the source-line breakpoints shipped last release. A breakpoint set on a line that holds no statement - a blank line, a comment, the middle of a multi-line expression - used to silently never fire. Now it SNAPS forward to the next line that does hold a statement, exactly like the reference browser: click near the code you mean and the breakpoint lands somewhere that actually runs. It is computed from the same compile-time line table, so it stays free when no breakpoint is set and touches nothing else. DevTools holds at 28; overall holds at 51.