Add doc-maintenance skill for periodic documentation accuracy audits

Skill detects documentation drift by scanning git history since last review,
cross-referencing shipped features against README, SPEC, and PRODUCT docs,
and opening PRs with minimal fixes. Includes audit checklist and section map
references.

Co-Authored-By: Paperclip <noreply@paperclip.ing>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.agents/skills/doc-maintenance/references/audit-checklist.md

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+# Doc Maintenance Audit Checklist
+
+Use this checklist when auditing each target document. For each item, compare
+against the change summary from git history.
+
+## README.md
+
+### Features table
+- [ ] Each feature card reflects a shipped capability
+- [ ] No feature cards for things that don't exist yet
+- [ ] No major shipped features missing from the table
+
+### Roadmap
+- [ ] Nothing listed as "planned" or "coming soon" that already shipped
+- [ ] No removed/cancelled items still listed
+- [ ] Items reflect current priorities (cross-check with recent PRs)
+
+### Quickstart
+- [ ] `npx paperclipai onboard` command is correct
+- [ ] Manual install steps are accurate (clone URL, commands)
+- [ ] Prerequisites (Node version, pnpm version) are current
+- [ ] Server URL and port are correct
+
+### "What is Paperclip" section
+- [ ] High-level description is accurate
+- [ ] Step table (Define goal / Hire team / Approve and run) is correct
+
+### "Works with" table
+- [ ] All supported adapters/runtimes are listed
+- [ ] No removed adapters still listed
+- [ ] Logos and labels match current adapter names
+
+### "Paperclip is right for you if"
+- [ ] Use cases are still accurate
+- [ ] No claims about capabilities that don't exist
+
+### "Why Paperclip is special"
+- [ ] Technical claims are accurate (atomic execution, governance, etc.)
+- [ ] No features listed that were removed or significantly changed
+
+### FAQ
+- [ ] Answers are still correct
+- [ ] No references to removed features or outdated behavior
+
+### Development section
+- [ ] Commands are accurate (`pnpm dev`, `pnpm build`, etc.)
+- [ ] Link to DEVELOPING.md is correct
+
+## doc/SPEC.md
+
+### Company Model
+- [ ] Fields match current schema
+- [ ] Governance model description is accurate
+
+### Agent Model
+- [ ] Adapter types match what's actually supported
+- [ ] Agent configuration description is accurate
+- [ ] No features described as "not supported" or "not V1" that shipped
+
+### Task Model
+- [ ] Task hierarchy description is accurate
+- [ ] Status values match current implementation
+
+### Extensions / Plugins
+- [ ] If plugins are shipped, no "not in V1" or "future" language
+- [ ] Plugin model description matches implementation
+
+### Open Questions
+- [ ] Resolved questions removed or updated
+- [ ] No "TBD" items that have been decided
+
+## doc/PRODUCT.md
+
+### Core Concepts
+- [ ] Company, Employees, Task Management descriptions accurate
+- [ ] Agent Execution modes described correctly
+- [ ] No missing major concepts
+
+### Principles
+- [ ] Principles haven't been contradicted by shipped features
+- [ ] No principles referencing removed capabilities
+
+### User Flow
+- [ ] Dream scenario still reflects actual onboarding
+- [ ] Steps are achievable with current features