Define Windows 95 and OS/2 assistant shell parity

[tsotchke]

Goal
Define and test the non-DOS shell contract before implementing Windows 95 or OS/2 assistant shells.

Acceptance criteria

• Shared pack parsing contract covers PACK.INI, HELP.TXT, USAGE.TXT, sprites/icons, USER.TXT, KB2, and pack-local model paths.
• Parity document states which DOS shell commands must exist on future Windows 95 and OS/2 shells.
• Host tests validate pack metadata without relying on DOS-only paths.
• No release claim is made for Windows or OS/2 execution until a scripted probe exists.

Evidence gate
python3 -m unittest tests.test_assistant_pack_contract tests.test_interactive_assistant_demo
python3 scripts/validate_assistant_pack_authoring.py
python3 scripts/verify_assistant_packs.py

Boundary
No physical hardware validation is claimed by this issue.