feat(claude): user_config defaults in command/agent prompts + governance alignment scan

[ErbolTakhirov]

Summary

This PR is a scoped v2 follow-up to the previous feat/userconfig-wiring attempt, rebuilt from current main to avoid cross-PR regressions.

It keeps only the intended architecture:

• Add user_config-based defaulting guidance in Claude command bodies.
• Add the same defaulting guidance in Claude agent bodies.
• Add arckit-claude/hooks/governance-scan.mjs checks for plugin default alignment gaps (Classification / Owner).

Included in This PR

1) Command Body Updates (Claude)

Command text now includes guidance to:

• Default [CLASSIFICATION] and [OWNER_NAME_AND_ROLE] from \${user_config.*} where available.
• Prompt the user when a default is unavailable.
• Apply Governance Framework Mode logic (UK Gov vs Generic) in body instructions.

2) Agent Body Updates (Claude)

Agent prompts follow the same pattern:

• Use \${user_config.*} defaults in prompt body logic.
• Fall back to user prompt when defaults are missing.
• Preserve governance-mode behavior in agent instructions.

3) Governance Scan Hook

Introduces arckit-claude/hooks/governance-scan.mjs behavior that:

• Reads plugin defaults from CLAUDE_PLUGIN_OPTION_* environment variables.
• Adds a Plugin Default Alignment Gaps section.
• Flags artifact-level metadata mismatches for:
  • Classification
  • Owner

Explicitly Out of Scope

To keep this PR merge-safe and aligned with prior review feedback, the following are intentionally excluded:

• Template-level \${user_config.*} substitution changes.
• Bulk template rewrites across plugin trees.
• scripts/converter.py placeholder rewrite/copy flows.
• Any arckit-paperclip/ script reintroductions or related regressions.
• Changes to:
  • arckit-claude/commands/pages.md
  • arckit-claude/templates/pages-template.html
  • arckit-claude/hooks/allow-mcp-tools.mjs
• Deletions/overwrites of recently merged guide/docs work.

Rationale

user_config interpolation is reliable in command/agent body text, but not in arbitrary template file contents loaded at runtime.
This PR therefore applies defaults only where substitution is guaranteed and avoids template-level substitution risk.

Validation Notes

• Rebuilt from current main to avoid silent reverts.
• Diff intentionally constrained to:
  • Claude command bodies
  • Claude agent bodies
  • governance scan hook
• No template/converter/paperclip regression surface included.