chore(skill): migrate skills to plugin format and update docs

Move existing skills from .claude/skills/ to skills/*/SKILL.md plugin
format. Update CLAUDE.md to reflect all skill commands. Add phase 2
implementation plan.

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

CLAUDE.md

@@ -7,7 +7,7 @@ An open-source tool combining LLM intelligence + static analysis to produce inte
 - **Monorepo** with pnpm workspaces
 - **packages/core** — Shared analysis engine (types, persistence, tree-sitter plugin, LLM prompt templates)
 - **packages/dashboard** — React + TypeScript web dashboard (React Flow, Monaco Editor, Zustand, TailwindCSS)
-- **packages/skill** — Claude Code skill (`/understand-chat` command)
+- **packages/skill** — Claude Code skills (`/understand-chat`, `/understand-diff`, `/understand-explain`, `/understand-onboard`)
 
 ## Key Commands
 - `pnpm install` — Install all dependencies

packages/skill/skills/understand-chat/SKILL.md

@@ -1,7 +1,7 @@
 ---
 name: understand-chat
-description: Ask questions about the current codebase using the knowledge graph
-arguments: query
+description: Use when you need to ask questions about a codebase or understand code using a knowledge graph
+argument-hint: [query]
 ---
 
 # /understand-chat
@@ -12,7 +12,7 @@ Answer questions about this codebase using the knowledge graph at `.understand-a
 
 1. Read the knowledge graph file at `.understand-anything/knowledge-graph.json` in the current project root
 2. If the file doesn't exist, tell the user to run `/understand` first to analyze the project
-3. Use the knowledge graph context to answer the user's query: "${ARGUMENTS}"
+3. Use the knowledge graph context to answer the user's query: "$ARGUMENTS"
 4. Reference specific files, functions, and relationships from the graph
 5. If the project has layers defined, explain which layer(s) are relevant
 6. Be concise but thorough -- link concepts to actual code locations

packages/skill/skills/understand-diff/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: understand-diff
-description: Analyze current git diff or PR against the knowledge graph to identify changes, impact, and risks
+description: Use when you need to analyze git diffs or pull requests to understand what changed, affected components, and risks
 ---
 
 # /understand-diff

packages/skill/skills/understand-explain/SKILL.md

@@ -1,7 +1,7 @@
 ---
 name: understand-explain
-description: Deep-dive explanation of a specific file or function using the knowledge graph
-arguments: path
+description: Use when you need a deep-dive explanation of a specific file, function, or module in the codebase
+argument-hint: [file-path]
 ---
 
 # /understand-explain
@@ -12,7 +12,7 @@ Provide a thorough, in-depth explanation of a specific code component.
 
 1. Read the knowledge graph file at `.understand-anything/knowledge-graph.json`
 2. If it doesn't exist, tell the user to run `/understand` first
-3. Find the component matching the path: "${ARGUMENTS}"
+3. Find the component matching the path: "$ARGUMENTS"
    - Supports file paths: `src/auth/login.ts`
    - Supports function notation: `src/auth/login.ts:verifyToken`
 4. Analyze the component in context:

packages/skill/skills/understand-onboard/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: understand-onboard
-description: Generate a structured onboarding guide for new team members using the knowledge graph
+description: Use when you need to generate an onboarding guide for new team members joining a project
 ---
 
 # /understand-onboard