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.

grammar.js

@@ -103,7 +103,7 @@ module.exports = grammar(bashGrammar, {
             "BeforeRun",
             "AfterRun",
           ),
-          field("label", optional(choice($.string, $.raw_string, $.word))),
+          optional(field("label", choice($.string, $.raw_string, $.word))),
           repeat($._terminated_statement),
           "End",
         ),
@@ -115,7 +115,7 @@ module.exports = grammar(bashGrammar, {
         1,
         seq(
           choice("Parameters", "Skip", "Pending", "Todo"),
-          field("label", optional(choice($.string, $.raw_string, $.word))),
+          optional(field("label", choice($.string, $.raw_string, $.word))),
           repeat($._terminated_statement),
           "End",
         ),