compiler-toolchain compatibility pass (permissive stubs, batch/features, Wine/native dispatch)

[xor2003]

High-level changes

1. Compatibility and stability

• Reduced hard aborts in permissive mode; unsupported paths now return graceful errors where possible.
• Improved LINK/BC5/TASM-related behavior.
• Added explicit DPMI diagnostic messaging for BC5/32RTM flows.
• Fixed path bounds/argument handling issues and related crashers.

2. Batch/runtime behavior

• Expanded batch command support for typical DOS compiler scripts.
• Improved case fallback and cd/path behavior in batch/toolchain scenarios.
• Improved environment passthrough for child DOS tool execution.

3. CLI and docs

• Added structured CLI options + toolchain presets/defaults.
• Updated README with clearer quick-start, defaults, and examples.
• Updated Makefile/test integration accordingly.

4. Host executable dispatch

• Added native dispatch for Linux executables.
• Added Wine delegation for Windows executables (PE/NE/LE/LX detection).

Why
Goal is to run legacy DOS compiler toolchains with fewer fatal exits and clearer diagnostics, while keeping kvikdos fast and minimal.

Validation summary

• Regression runs on target compilers/tooling (MSC/MASM/Borland/others in local tool directories).
• Added/updated automated tests (make test) and docs for reproducible verification.
• Static/runtime checks executed (cppcheck/clang analyzer/sanitizer/valgrind workflow documented).