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/mcp-tools-reference.md

@@ -0,0 +1,69 @@
+# MCP Tools Reference
+
+## pandas Tools
+
+| Tool | Description |
+|------|-------------|
+| `read_csv` | Load CSV file into DataFrame |
+| `read_parquet` | Load Parquet file into DataFrame |
+| `read_json` | Load JSON/JSONL file into DataFrame |
+| `to_csv` | Export DataFrame to CSV |
+| `to_parquet` | Export DataFrame to Parquet |
+| `describe` | Get statistical summary (count, mean, std, min, max) |
+| `head` | Preview first N rows |
+| `tail` | Preview last N rows |
+| `filter` | Filter rows by condition |
+| `select` | Select specific columns |
+| `groupby` | Aggregate data by columns |
+| `join` | Join two DataFrames |
+| `list_data` | List all loaded DataFrames |
+| `drop_data` | Remove DataFrame from memory |
+
+## PostgreSQL Tools
+
+| Tool | Description |
+|------|-------------|
+| `pg_connect` | Establish database connection |
+| `pg_query` | Execute SELECT query, return DataFrame |
+| `pg_execute` | Execute INSERT/UPDATE/DELETE |
+| `pg_tables` | List tables in schema |
+| `pg_columns` | Get column info for table |
+| `pg_schemas` | List available schemas |
+
+## PostGIS Tools
+
+| Tool | Description |
+|------|-------------|
+| `st_tables` | List tables with geometry columns |
+| `st_geometry_type` | Get geometry type for column |
+| `st_srid` | Get SRID for geometry column |
+| `st_extent` | Get bounding box for geometry |
+
+## dbt Tools
+
+| Tool | Description |
+|------|-------------|
+| `dbt_parse` | Validate project (ALWAYS RUN FIRST) |
+| `dbt_run` | Execute models |
+| `dbt_test` | Run tests |
+| `dbt_build` | Run + test together |
+| `dbt_compile` | Compile SQL without execution |
+| `dbt_ls` | List dbt resources |
+| `dbt_docs_generate` | Generate documentation manifest |
+| `dbt_lineage` | Get model dependencies |
+
+## Tool Selection Guidelines
+
+**For data loading:**
+- Files: `read_csv`, `read_parquet`, `read_json`
+- Database: `pg_query`
+
+**For data exploration:**
+- Schema: `describe`, `pg_columns`, `st_tables`
+- Preview: `head`, `tail`
+- Available data: `list_data`, `pg_tables`
+
+**For dbt operations:**
+- Always start with `dbt_parse` for validation
+- Use `dbt_lineage` for dependency analysis
+- Use `dbt_compile` to see rendered SQL