feat(cli): add skill command for SKILL.md generation

[bug-ops]

Summary

• Add skill CLI command to generate Claude Code skill files (SKILL.md) from progressive loading TypeScript files
• Refactor main.rs into modular cli.rs/runner.rs structure for better maintainability
• Improve mcp-skill README with proper MSRV documentation and GitHub callouts

Changes

New Features

• mcp-execution-cli skill command with options:
  • --server, -s - Server identifier (required)
  • --servers-dir - Custom servers directory
  • --output, -o - Custom output path
  • --skill-name - Custom skill name
  • --hint - Use case hints (repeatable)
  • --overwrite - Overwrite existing SKILL.md

Security

• Path traversal detection using Component::ParentDir analysis
• Symlink escape protection via canonicalize() + starts_with() validation
• Output path validation for custom paths
• DoS protection (max 500 files, max 1MB per file)

Code Quality

• Refactored 500+ line main.rs into focused modules
• Added comprehensive tests for command parsing and security functions
• Updated documentation with MCP server recommendation

Test Plan

• All 611 tests pass
• Clippy warnings resolved
• Security review passed
• Path traversal tests added

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.81865% with 10 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/mcp-skill/src/parser.rs	92.48%	10 Missing ⚠️

@@            Coverage Diff             @@
##           master      #40      +/-   ##
==========================================
+ Coverage   92.41%   92.80%   +0.38%     
==========================================
  Files          21       22       +1     
  Lines        4749     4779      +30     
==========================================
+ Hits         4389     4435      +46     
+ Misses        360      344      -16     

Flag	Coverage Δ
unittests	92.80% <94.81%> (+0.38%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
crates/mcp-server/src/service.rs	83.25% <100.00%> (-0.89%)	⬇️
crates/mcp-server/src/types.rs	100.00% <ø> (ø)
crates/mcp-skill/src/context.rs	98.92% <100.00%> (ø)
crates/mcp-skill/src/template.rs	98.18% <100.00%> (ø)
crates/mcp-skill/src/types.rs	100.00% <100.00%> (ø)
crates/mcp-skill/src/parser.rs	97.61% <92.48%> (ø)

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