Add new-repository bootstrap runbook and templates

[ss-o]

Summary

Add the missing Week 2 bootstrap material from the LLM-management plan so new z-shell repositories start with the expected instructions, labels, CI, license, README skeleton, and plugin/annex/module structure.

Scope

• add runbooks/new-plugin.md or a broader new-repository bootstrap runbook
• add or document template structure for plugin, annex, and module repositories
• decide which template assets live in this repo versus dedicated template repositories
• include AGENTS/Copilot pointer, CI, license, README, and issue/PR template expectations

Acceptance criteria

• maintainers can create a new plugin or annex without copying files ad hoc
• the runbook links to canonical labels, workflow templates, and PATTERNS.md
• any deferred template repository creation is split into separate follow-up issues

Suggested tracker fields

• Item Type: Chore
• Impact: Medium
• Effort: M
• Status: Triage