feat: add mcp documentation skill for spec-aware development (#609)

Add a Claude Code skill (`.claude/skills/mcp-docs/`) that provides live
MCP documentation and specification context

## Motivation and Context
The modelcontextprotocol.io site provides both an [MCP
server](https://modelcontextprotocol.io/mcp) and an
[llms.txt](https://modelcontextprotocol.io/llms.txt) index for
machine-readable access to the documentation. This skill leverages both
to give Claude live access to the current spec during development.

## How Has This Been Tested?
The skill was evaluated on 3 realistic scenarios (implementation, code
review, spec question) comparing with-skill vs without-skill baseline:
- **Pass rate**: 100% vs 67% — skill consistently cites spec sources and
uses RFC 2119 language
- **Token efficiency**: 41% fewer tokens on average (44k vs 75k) — goes
directly to spec instead of reverse-engineering from codebase
- **Accuracy**: with-skill discovered URL mode elicitation (new in spec
2025-11-25) that baseline missed entirely
- **Description triggering**: optimized through 5 iterations of
automated trigger evaluation against 20 test prompts

## Breaking Changes
None

## Types of changes
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [x] Documentation update

## Checklist
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed

.gitignore

@@ -56,7 +56,7 @@ node_modules
 dist
 
 ### SWE agents ###
-.claude/
+.claude/settings.local.json
 .junie/
 
 ### Conformance test results ###