Remove GDB/MI debugger host support

[gloveboxes]

Summary

ntvcm is no longer used as a debugger host. Remove the embedded GDB Machine Interface implementation and all app-facing integration for that role.

Changes

• remove the GDB/MI command parser, protocol responses, metadata loader, expression evaluator, stack-frame handling, and variable-object support
• remove --interpreter=mi startup and help-text support
• remove CPU breakpoint, pause, continue, and single-step state and APIs
• simplify console input/output and the emulation loop to the normal execution path
• delete the obsolete tests/debugger_mi.py regression suite
• retain unrelated native compiler symbols, debug/release build flavors, execution tracing, and profiling

Validation

• compiled and linked ntvcm.cxx and x80.cxx successfully with G++
• ran 8080PRE.COM successfully under a hard timeout
• verified workspace diagnostics are clean
• searched source, tests, scripts, README files, workflows, hidden configuration, linked symbols, binary strings, and public help output for residual GDB/MI debugger-host references
• verified patch whitespace with CRLF-aware Git settings

[gloveboxes]

Closing so the branch owner can open the upstream pull request directly.