[skill+prompt] Add mapbox-style-quality skill and prepare-style-for-production prompt

Adds comprehensive style quality validation capabilities:

Skill:
- Created mapbox-style-quality skill document (390+ lines)
- Pre-production checklist and validation best practices
- Guidance on expression validation, GeoJSON validation, and accessibility
- Optimization strategies and workflow recommendations
- Integration patterns for Git hooks, CI/CD, and code review

Prompt:
- Created prepare-style-for-production prompt
- Orchestrates validation workflow using 5 quality tools:
  * validate_expression_tool - Validate expressions in filters/paint/layout
  * validate_geojson_tool - Validate GeoJSON sources
  * check_color_contrast_tool - WCAG accessibility compliance
  * optimize_style_tool - Remove redundancies and optimize
  * compare_styles_tool - Compare versions (implicit in workflow)
- Configurable WCAG level (AA/AAA) and optional optimization skip
- Generates comprehensive quality report with deployment readiness assessment

Testing:
- 15 test cases for PrepareStyleForProductionPrompt
- All 386 tests passing
- Updated prompt registry tests

Documentation:
- Updated README with new skill listing
- Added prompt documentation with usage examples
- Cross-referenced skill and prompt

Related PRs:
- PR #50: validate_geojson_tool
- PR #51: validate_expression_tool
- PR #52: compare_styles_tool
- PR #53: check_color_contrast_tool
- PR #54: optimize_style_tool

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

Author: mattpodwysocki

README.md

@@ -463,6 +463,7 @@ This repository includes [Agent Skills](https://agentskills.io) that provide dom
 - **🔐 mapbox-token-security**: Token management, scope control, URL restrictions, rotation strategies
 - **📐 mapbox-style-patterns**: Common style patterns and layer configurations for typical scenarios
 - **🔧 mapbox-integration-patterns**: Framework-specific integration patterns for React, Vue, Svelte, Angular, and vanilla JS
+- **✅ mapbox-style-quality**: Expert guidance on validating, optimizing, and ensuring quality of Mapbox styles through validation, accessibility checks, and optimization
 
 Skills complement the MCP server by providing expertise (how to think about design) while tools provide capabilities (how to execute actions).
 
@@ -673,6 +674,39 @@ Arguments:
   color_scheme: "sequential"
 ```
 
+### prepare-style-for-production
+
+Comprehensive quality validation workflow for Mapbox styles before production deployment.
+
+**Arguments:**
+
+- `style_id_or_json` (required): Either a Mapbox style ID or complete style JSON
+- `skip_optimization` (optional): Set to "true" to skip style optimization (default: false)
+- `wcag_level` (optional): WCAG compliance level: "AA" or "AAA" (default: "AA")
+
+**What it does:**
+
+1. Loads the style (retrieves from Mapbox or parses JSON)
+2. Validates all expressions (filters, paint properties, layout properties)
+3. Validates GeoJSON sources for coordinate and structure errors
+4. Checks color contrast for text layers (WCAG compliance)
+5. Optimizes the style (removes redundancies, simplifies expressions)
+6. Generates a comprehensive quality report with deployment readiness assessment
+
+**Example usage:**
+
+```
+Use prompt: prepare-style-for-production
+Arguments:
+  style_id_or_json: "username/my-style-id"
+  wcag_level: "AA"
+  skip_optimization: "false"
+```
+
+**Related:**
+
+See the [mapbox-style-quality skill](skills/mapbox-style-quality/SKILL.md) for detailed guidance on when to use validation tools, best practices, and optimization strategies.
+
 ## Resources
 
 This server exposes static reference documentation as MCP Resources. While these are primarily accessed through the `get_reference_tool`, MCP clients that fully support the resources protocol can access them directly.