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/commands/dbt-test.md

@@ -1,18 +1,13 @@
 # /dbt-test - Run dbt Tests
 
+## Skills to Load
+- skills/dbt-workflow.md
+- skills/mcp-tools-reference.md
+- skills/visual-header.md
+
 ## Visual Output
 
-When executing this command, display the plugin header:
-
-```
-┌──────────────────────────────────────────────────────────────────┐
-│  📊 DATA-PLATFORM · dbt Tests                                     │
-└──────────────────────────────────────────────────────────────────┘
-```
-
-Then proceed with the tests.
-
-Execute dbt tests with formatted pass/fail results.
+Display header: `DATA-PLATFORM - dbt Tests`
 
 ## Usage
 
@@ -22,75 +17,17 @@ Execute dbt tests with formatted pass/fail results.
 
 ## Workflow
 
-1. **Pre-validation** (MANDATORY):
-   - Use `dbt_parse` to validate project first
-   - If validation fails, show errors and STOP
+Execute `skills/dbt-workflow.md` test workflow:
 
-2. **Execute tests**:
-   - Use `dbt_test` with provided selection
-   - Capture all test results
-
-3. **Format results**:
-   - Group by test type (schema vs. data)
-   - Show pass/fail status with counts
-   - Display failure details
-
-## Report Format
-
-```
-=== dbt Test Results ===
-Project: my_project
-Selection: tag:critical
-
---- Summary ---
-Total: 24 tests
-PASS:  22 (92%)
-FAIL:  1  (4%)
-WARN:  1  (4%)
-SKIP:  0  (0%)
-
---- Schema Tests (18) ---
-[PASS] unique_dim_customers_customer_id
-[PASS] not_null_dim_customers_customer_id
-[PASS] not_null_dim_customers_email
-[PASS] accepted_values_dim_customers_status
-[FAIL] relationships_fct_orders_customer_id
-
---- Data Tests (6) ---
-[PASS] assert_positive_order_amounts
-[PASS] assert_valid_dates
-[WARN] assert_recent_orders (threshold: 7 days)
-
---- Failure Details ---
-Test: relationships_fct_orders_customer_id
-Type: schema (relationships)
-Model: fct_orders
-Message: 15 records failed referential integrity check
-Query: SELECT * FROM fct_orders WHERE customer_id NOT IN (SELECT customer_id FROM dim_customers)
-
---- Warning Details ---
-Test: assert_recent_orders
-Type: data
-Message: No orders in last 7 days (expected for dev environment)
-Severity: warn
-```
-
-## Selection Syntax
-
-| Pattern | Meaning |
-|---------|---------|
-| (none) | Run all tests |
-| `model_name` | Tests for specific model |
-| `+model_name` | Tests for model and upstream |
-| `tag:critical` | Tests with tag |
-| `test_type:schema` | Only schema tests |
-| `test_type:data` | Only data tests |
+1. **Pre-validation** (MANDATORY): Run `dbt_parse` first
+2. **Execute tests**: Use `dbt_test` with selection
+3. **Format results**: Group by test type, show pass/fail/warn counts
 
 ## Options
 
 | Flag | Description |
 |------|-------------|
-| `--warn-only` | Treat failures as warnings (don't fail CI) |
+| `--warn-only` | Treat failures as warnings |
 
 ## Examples
 
@@ -98,34 +35,9 @@ Severity: warn
 /dbt-test                          # Run all tests
 /dbt-test dim_customers            # Tests for specific model
 /dbt-test tag:critical             # Run critical tests only
-/dbt-test +fct_orders              # Test model and its upstream
 ```
 
-## Test Types
+## Required MCP Tools
 
-### Schema Tests
-Built-in tests defined in `schema.yml`:
-- `unique` - No duplicate values
-- `not_null` - No null values
-- `accepted_values` - Value in allowed list
-- `relationships` - Foreign key integrity
-
-### Data Tests
-Custom SQL tests in `tests/` directory:
-- Return rows that fail the assertion
-- Zero rows = pass, any rows = fail
-
-## Exit Codes
-
-| Code | Meaning |
-|------|---------|
-| 0 | All tests passed |
-| 1 | One or more tests failed |
-| 2 | dbt error (parse failure, etc.) |
-
-## Available Tools
-
-Use these MCP tools:
 - `dbt_parse` - Pre-validation (ALWAYS RUN FIRST)
 - `dbt_test` - Execute tests (REQUIRED)
-- `dbt_build` - Alternative: run + test together