refactor: extract skills from commands across 8 plugins

Refactored commands to extract reusable skills following the
Commands → Skills separation pattern. Each command is now <50 lines
and references skill files for detailed knowledge.

Plugins refactored:
- claude-config-maintainer: 5 commands → 7 skills
- code-sentinel: 3 commands → 2 skills
- contract-validator: 5 commands → 6 skills
- data-platform: 10 commands → 6 skills
- doc-guardian: 5 commands → 6 skills (replaced nested dir)
- git-flow: 8 commands → 7 skills

Skills contain: workflows, validation rules, conventions,
reference data, tool documentation

Commands now contain: YAML frontmatter, agent assignment,
skills list, brief workflow steps, parameters

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugins/data-platform/skills/setup-workflow.md

@@ -0,0 +1,108 @@
+# Setup Workflow
+
+## Important Context
+
+- **This workflow uses Bash, Read, Write, AskUserQuestion tools** - NOT MCP tools
+- **MCP tools won't work until after setup + session restart**
+- **PostgreSQL and dbt are optional** - pandas tools work without them
+
+## Phase 1: Environment Validation
+
+### Check Python Version
+```bash
+python3 --version
+```
+Requires Python 3.10+. If below, stop and inform user.
+
+## Phase 2: MCP Server Setup
+
+### Locate MCP Server
+Check both paths:
+```bash
+# Installed marketplace
+ls -la ~/.claude/plugins/marketplaces/leo-claude-mktplace/mcp-servers/data-platform/
+
+# Source
+ls -la ~/claude-plugins-work/mcp-servers/data-platform/
+```
+
+### Check/Create Virtual Environment
+```bash
+# Check
+ls -la /path/to/mcp-servers/data-platform/.venv/bin/python
+
+# Create if missing
+cd /path/to/mcp-servers/data-platform
+python3 -m venv .venv
+source .venv/bin/activate
+pip install --upgrade pip
+pip install -r requirements.txt
+deactivate
+```
+
+## Phase 3: PostgreSQL Configuration (Optional)
+
+### Config Location
+`~/.config/claude/postgres.env`
+
+### Config Format
+```bash
+# PostgreSQL Configuration
+POSTGRES_URL=postgresql://user:pass@host:5432/db
+```
+
+Set permissions: `chmod 600 ~/.config/claude/postgres.env`
+
+### Test Connection
+```bash
+source ~/.config/claude/postgres.env && python3 -c "
+import asyncio, asyncpg
+async def test():
+    conn = await asyncpg.connect('$POSTGRES_URL', timeout=5)
+    ver = await conn.fetchval('SELECT version()')
+    await conn.close()
+    print(f'SUCCESS: {ver.split(\",\")[0]}')
+asyncio.run(test())
+"
+```
+
+## Phase 4: dbt Configuration (Optional)
+
+dbt is **project-level** (auto-detected via `dbt_project.yml`).
+
+For subdirectory projects, set in `.env`:
+```
+DBT_PROJECT_DIR=./transform
+DBT_PROFILES_DIR=~/.dbt
+```
+
+### Check dbt Installation
+```bash
+dbt --version
+```
+
+## Phase 5: Validation
+
+### Verify MCP Server
+```bash
+cd /path/to/mcp-servers/data-platform
+.venv/bin/python -c "from mcp_server.server import DataPlatformMCPServer; print('OK')"
+```
+
+## Memory Limits
+
+Default: 100,000 rows per DataFrame
+
+Override in project `.env`:
+```
+DATA_PLATFORM_MAX_ROWS=500000
+```
+
+For larger datasets:
+- Use chunked processing (`chunk_size` parameter)
+- Filter data before loading
+- Store to Parquet for efficient re-loading
+
+## Session Restart
+
+After setup, restart Claude Code session for MCP tools to become available.