Mixed SOURCE/ASM mode for stepping through code.

**Is your feature request related to a problem? Please describe.**
In the embedded world (and Linux word) when debugging it is often equired to step through disassembly. Having a mode that allows you to have a mixed mode would be very helpful.

**Describe the solution you'd like**
A clear and concise description of what you want to happen.

MIXED asm/source display would be helpful.

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

A disassembly window would work nicely also - provided one can click and set breakpoints in that window.

**Additional context**
Add any other context or screenshots about the feature request here.

Begin with the TypeScript frontend's existing source display and breakpoint UI, then check how GDB output is surfaced. The issue names no files or tests; done means defining and implementing a mixed source/assembly view or disassembly window with breakpoint interaction, along with a clear way to verify the behavior.

Written by the indexing model from the issue text.