[docs] Establish Autonomous Deployment Contract for self-deployment #145

[liujuanjuan1984]

Description

This PR establishes the Autonomous Deployment Contract in the core documentation (README.md, SECURITY.md, and script-specific READMEs), resolving the conceptual part of umbrella issue #145.

By moving from interactive deployment to a machine-readable contract, we enable consumers to orchestrate isolated instance pairs programmatically while maintaining the single-tenant trust boundary.

Key Changes

• README.md: Defined the 'Single-Tenant Self-Deployment' design principle and the Autonomous Deployment Contract.
• SECURITY.md: Updated the security boundary to explicitly mention parameterized self-deployment and its role in tenant isolation.
• scripts/deploy_readme.md: Renamed and refined the 'Autonomous Deployment Contract' section, specifying baseline exit code categories (aligned with [Priority: Med] [Ops] 补齐 deploy 自动化契约：非交互预检、健康验收与参数校验 #148).
• scripts/deploy_light_readme.md: Aligned terminology and updated to reflect the convergence of deploy_light.sh into a foreground launcher (aligned with [Priority: High] [Ops] 将 deploy_light 收敛为前台 launcher，并将 nohup/pm2 交给调用方 #181).

Relation

• Closes [Priority: High] [Feature] 支持消费方按需自部署 opencode-a2a-server（参数化拉起） #145
• Relates to [Priority: Med] [Ops] 补齐 deploy 自动化契约：非交互预检、健康验收与参数校验 #148
• Relates to [Priority: High] [Ops] 将 deploy_light 收敛为前台 launcher，并将 nohup/pm2 交给调用方 #181