feat: document quality gate hook — advisory content validation

[DavidROliverBA]

Summary

PostToolUse hook that validates ARC document content quality after every write. Advisory only — never blocks, surfaces warnings as context so Claude can offer to fix issues.

• Document control completeness — detects placeholder text ([Author], TBD, TODO, XXX)
• Requirement ID format — flags malformed IDs (e.g., BR-1 instead of BR-001)
• Empty section detection — headings with no content below them
• Cross-reference integrity — references to ARC documents that don't exist in the project

Files Changed

File	Change
arckit-claude/hooks/document-quality-gate.mjs	New — PostToolUse hook
arckit-claude/hooks/hooks.json	Register hook after update-manifest
docs/guides/document-quality-gate.md	New — usage guide

Design Decisions

• Advisory, not blocking — architects should never be prevented from saving work. Warnings surface as context for Claude to address.
• Uses existing extractors — imports extractDocType from hook-utils.mjs and DOC_TYPES from doc-types.mjs
• Scoped to ARC documents — only fires on ARC-*.md files under projects/

Test plan

• JSON validation of hooks.json
• ESM import validation
• Write an ARC document with placeholder text — verify warnings surface
• Write an ARC document with clean content — verify no warnings
• Write a non-ARC file — verify silent pass-through

🤖 Generated with Claude Code

[tractorjuice]

Superseded by #150, which includes your original quality gate hook, hooks.json registration, and guide plus:

Lint fixes:

• Added text language specifier to 4 fenced code blocks in docs/guides/document-quality-gate.md (MD040)
• Added blank lines before lists in 6 Gemini agent files (MD032): arckit-aws-research.md, arckit-azure-research.md, arckit-datascout.md, arckit-framework.md, arckit-gcp-research.md, arckit-research.md

Your original commit is preserved as-is in #150. Thanks for the contribution!