docs(launch): create maintainer install and trust guide

[JSONbored]

Parent phase: #238
Parent roadmap: #127

Problem

Maintainers need a direct guide for installation, command authorization, preview behavior, private/public boundaries, extension usage, and how to reject low-quality Gittensory-driven PRs.

Acceptance criteria

• Guide explains GitHub App setup, maintainer controls, extension states, public-safe previews, and audit expectations.
• Guide explicitly says UI/frontend/extension PRs need screenshots or recordings for acceptance.
• Guide separates CI/check state from reviewer/mergeability state.

Validation expected

• Docs build/lint passes if applicable.
• Screenshots or diagrams are included where UI/extension flows are described.

UI evidence gate

Any visible web, browser-extension, or GitHub-overlay change must include maintainer-reviewable screenshots or a short recording covering the changed states. A checked template box without actual visual evidence is not enough.

Public-output safety criteria

• Public text is sanitized before reaching GitHub comments, issue bodies, PR bodies, extension-visible public panels, or copied public snippets.
• Tests cover forbidden wallet/hotkey, reward-estimate, trust-score, public-score-prediction, private-reviewability, private-scoreability, and farming-language leakage.

Cross-cutting acceptance criteria

• Preserve the repo quality gate: npm run test:ci, 97%+ global coverage, and the local branch coverage target for touched code.
• Keep public/private boundaries explicit. Public GitHub output must not expose wallets, hotkeys, reward estimates, raw trust scores, public score predictions, private reviewability, private scoreability context, or farming language.
• Add/update focused tests for the changed behavior instead of relying on green checks alone.