docs: define Maya E2E consumer contract

[BramVR]

Summary

• define the consuming-repository contract for the Maya plug-in E2E skill
• keep deterministic scenarios in product repositories
• keep private host and trust configuration operator-owned

[Copilot]

Pull request overview

Defines a clear “consuming repo contract” for using the maya-plugin-e2e skill, separating deterministic scenario/test inputs (kept in product repos) from operator-owned/private host and trust configuration (kept outside repos).

Changes:

• Add a “Consuming Repo Contract” section describing what each consuming repository must own (scenario YAML, scripts, docs, routing).
• Document guidance to keep host/trust configuration outside the consuming repo.

Comments suppressed due to low confidence (1)

skills/maya-plugin-e2e/SKILL.md:38

• This section introduces “Host Config” (title case) and a hard requirement on MAYA_STALL_HOST_CONFIG, but elsewhere the skill uses “host config” and the --host-config flag. To avoid confusion, keep casing consistent and document selection in a way that matches the commands shown (with env var usage as an optional setup detail).

Keep Host Config outside the repo. Prefer a stable operator-owned path such as
`~/.config/maya-stall/hosts.yaml`, selected through `MAYA_STALL_HOST_CONFIG`.
The skill owns the workflow; the consuming repo owns product assertions; the
host config owns private infrastructure and trust policy.

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