fix(cli): update help examples binary name

[sarvesh1327]

Summary

• Update clap help examples for introspect, generate, and skill to use the published mcp-execution-cli binary name.
• Add a regression test that renders long help for those subcommands and rejects the old mcp-cli examples.

Test Plan

• cargo test -p mcp-execution-cli test_cli_help_examples_use_published_binary_name -- --nocapture
• cargo test -p mcp-execution-cli
• cargo fmt --all --check
• cargo clippy -p mcp-execution-cli --all-targets -- -D warnings
• Manual help checks for introspect, generate, and skill

Closes #93

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@            Coverage Diff             @@
##           master      #98      +/-   ##
==========================================
+ Coverage   89.82%   89.84%   +0.01%     
==========================================
  Files          33       33              
  Lines        7817     7830      +13     
==========================================
+ Hits         7022     7035      +13     
  Misses        795      795              

Flag	Coverage Δ
mcp-cli	89.84% <100.00%> (+0.01%)	⬆️
mcp-codegen	89.84% <100.00%> (+0.01%)	⬆️
mcp-core	89.84% <100.00%> (+0.01%)	⬆️
mcp-files	89.84% <100.00%> (+0.01%)	⬆️
mcp-introspector	89.84% <100.00%> (+0.01%)	⬆️
mcp-server	89.84% <100.00%> (+0.01%)	⬆️
mcp-skill	89.84% <100.00%> (+0.01%)	⬆️

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Files with missing lines	Coverage Δ
crates/mcp-cli/src/cli.rs	94.55% <100.00%> (+0.37%)	⬆️

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