Remove stale legacy documentation and DOSBox MCP

[nolanvenhola]

What changed

• Removes all 61 Markdown files from the speculative ndisasm documentation tree.
• Removes all 18 Markdown files from the historical TASM documentation tree.
• Removes the unused and broken DOSBox-MCP implementation (5 files).
• Removes stale references from the public README, project instructions, retained audit ledgers, and supporting guides.
• Keeps resource documentation, MASM documentation and audit artifacts, WASM parity records, TASM working ledgers, and Unicorn guides.

The untracked SESSION_HANDOFF.md was also removed locally as requested; it was never part of Git and therefore is not represented in this PR.

Why

These documentation trees predate the canonical MASM reconstruction and completed C/WebAssembly port. They contained speculative or obsolete guidance that competed with the current sources of truth. The DOSBox-MCP server was broken, unused, and explicitly prohibited by project guidance.

Validation

• git diff --cached --check`n- Repository-wide search finds no surviving reference to either deleted documentation tree or the retired MCP implementation.
• Local Markdown-link audit found no links broken by these deletions; eight unrelated pre-existing broken links remain in generated indexes and bundled third-party documentation.