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.

test/spec/18.const_directive_spec.sh

@@ -1,4 +1,4 @@
-#shellcheck shell=sh
+# shellcheck shell=sh
 
 %const NAME: value
 # shellcheck disable=SC2288
@@ -7,11 +7,11 @@
 
 # %const (% is short hand) directive is define constant value.
 # The characters that can be used for variable name is upper capital, number
-# and underscore only. It can not be define inside of the example group or
+# and underscore only. It cannot be define inside of the example group or
 # the example.
 #
 # The timing of evaluation of the value is the specfile translation process.
-# So you can access shellspec variables, but you can not access variable or
+# So you can access shellspec variables, but you cannot access variable or
 # function in the specfile.
 #
 # This feature assumed use with conditional skip. The conditional skip may runs