Add memory files for review-plan and review-spec skills

Skill documentation for the new plan/spec review skills. Each file
covers purpose, usage, how it works, referenced best practice files,
and gotchas.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

memory/skill-review-plan.md

@@ -0,0 +1,29 @@
+# Skill: review-plan
+
+## Purpose
+Reviews a plan file (*-PLAN.md) against best practices before implementation begins. Catches security gaps, missing specs, untested assumptions, and API design issues early -- when they're cheap to fix.
+
+## Usage
+```
+/review-plan M2-auth-PLAN.md
+/review-plan          # prompts to select from *-PLAN.md files
+```
+
+## How it works
+1. Loads 5 best practice files: api-design, llm-code-security, spec-driven-development, test-driven-development, security-architecture
+2. Reads the specified plan file
+3. Evaluates against a 6-area checklist: security by design, API design, LLM code security, spec-driven development, test-driven development, operational readiness
+4. Outputs a scorecard, critical gaps, recommendations, and acknowledgment of what's done well
+
+## Best practice files referenced
+- `~/dev/claude/projects/best-practices/api-design.md`
+- `~/dev/claude/projects/best-practices/llm-code-security.md`
+- `~/dev/claude/projects/best-practices/spec-driven-development.md`
+- `~/dev/claude/projects/best-practices/test-driven-development.md`
+- `~/dev/claude/projects/best-practices/security-architecture.md`
+- Plus any tech-stack-specific files from the index
+
+## Gotchas
+- Read-only skill (allowed-tools: Read, Glob, Grep, Bash cat/ls/find). Cannot edit files.
+- Relies on best-practices repo being cloned at `~/dev/claude/projects/best-practices/`
+- The `~/` path in the bang-command generates a validator warning but works in practice