[dev]: Adopt and enforce Zsh Plugin Standard 2 #557

Outcome

Adopt the revised portable Zsh Plugin Standard across organization policy,
plugin scaffolding, review guidance, testing requirements, and CI without
duplicating the canonical technical rules from the wiki.

Scope

• Draft a PROPOSED ADR for clean-break organization adoption.
• Update routed Zsh plugin and scripting guidance.
• Extend the machine-readable policy and its deterministic validator.
• Align the plugin reviewer, new-plugin skill, entrypoint template, README
  template, PATTERNS.md, and new-repository runbook.
• Update testing policy so maintained plugins prove lifecycle behavior.
• Require exact released zsh-lint and ZUnit pins after those tools publish
  the necessary contracts.
• Complete the instruction-update impact review and private route checks.

Non-goals

• Do not create a second organization-owned technical plugin standard.
• Do not retain legacy compatibility guidance for refactored plugins.
• Do not claim runtime lifecycle proof from static analysis.

Acceptance criteria

• The ADR is proposed and receives a separate maintainer acceptance decision.
• All organization surfaces link to one canonical public contract.
• A newly scaffolded plugin passes static and runtime checks unchanged.
• Templates create no scattered public configuration parameters or shared
  Plugins registration.
• Public and private instruction validators pass.
• CI guidance uses exact released tool pins.