fix: apply CodeRabbit nitpick suggestions and improve code quality

- Fix grammar.js TypeScript errors by correcting optional field usage
- Update .yamlignore to use more robust glob pattern (**/node_modules/**)
- Remove hard-coded test count from README.md for maintainability
- Fix shellcheck directive format (add space after #) in all test specs
- Fix typos throughout test specifications:
  - 'can not' → 'cannot'
  - 'expantion' → 'expansion'
  - 'singnal' → 'signal'
  - 'It mean' → 'It means'
- Update CODE_OF_CONDUCT.md HTTP links to HTTPS
- Update tree-sitter parse command to use --scope instead of --language
- Add comments to .mega-linter.yml explaining disabled linters

All grammar tests still pass (61/61) and the parser functions correctly
with the updated tree-sitter CLI v0.25.0.

.github/workflows/test.yml

@@ -124,7 +124,7 @@ jobs:
           End
           EOF
 
-          npx tree-sitter parse --language=shellspec test_sample.shellspec --quiet || {
+          npx tree-sitter parse --scope=source.shellspec test_sample.shellspec --quiet || {
             echo "❌ Parser failed on sample ShellSpec code"
             exit 1
           }