feat: automatic advisory design-review pass (validator + challenger)

[azmym]

Summary

Adds an automatic, advisory design-review pass: whenever a design/plan artifact is written or native plan mode exits, the plugin asks Claude to dispatch gemini-validator (VALIDATE_DESIGN) and gemini-challenger (CHALLENGE_DESIGN) over it. Closes the gap where a brainstorming spec written to disk got no automatic validate-and-challenge pass (only native plan mode did, and only the validator).

Implements docs/superpowers/specs/2026-06-02-design-review-pass-design.md.

What changed

• New PostToolUse(Write|Edit) hook (hooks/design-review.sh): path-matches design artifacts (*-design.md, *-plan.md, files under specs//plans/, DESIGN.md, PLAN.md; overridable via CLAUDE_PLUGIN_GEMINI_DESIGN_GLOBS), dedups by file content SHA-256 so cosmetic re-edits do not re-fire, and dispatches both agents as an advisory pass.
• Native plan-mode exit (plan-complete.sh) keeps its existing blocking validator and gains an advisory challenger.
• Per-dispatch advisory-vs-blocking routing: dispatching hooks write a per-agent pending/<agent>.mode marker; subagent-verdict-handler.sh consumes it. advisory means a fail/block verdict surfaces but exits 0; blocking (the default when no marker exists) keeps the pre-existing plan-validator and done-claim gates exiting 2. No regression to existing gates.
• New build_advisory_directive primitive so advisory consults omit the "Block until..." footer.
• Part of the uncounted hook channel: exempt from the one-consult-per-turn cap, silenced by CLAUDE_PLUGIN_GEMINI_DISABLE_HOOKS / brainstorm.off. Documented in gemini-consult skill and using-gemini rule.
• Bumped to 0.6.0, CHANGELOG updated.

Test Plan

• Full bats suite: 117 passed, 0 failed (was 83; +34 new tests).
• New coverage: glob matching (+ override), content-hash dedup, advisory-vs-blocking verdict routing, plan-complete advisory challenger, hooks.json registration, advisory-directive footer omission.
• Backward-compat verified: plan-validator and stop-done-claim still exit 2 on fail (default-blocking when no marker).
• No em/en dashes in the diff.
• Implemented via subagent-driven TDD; each batch passed spec + code-quality review, plus a final whole-feature review (verdict: ready to merge).

After merge, tag v0.6.0 to let the release workflow publish it. A fresh Claude Code session is required to load the new hook + agent wiring.