Fix review comments: update docs, clean up test whitespace, add sub-expression test

Co-authored-by: wagenet <9835+wagenet@users.noreply.github.com>

Author: Copilot

.gitignore

@@ -4,6 +4,7 @@ logs
 
 # Dependencies
 node_modules
+package-lock.json
 
 # Misc
 .eslintcache

docs/rules/template-no-deprecated.md

@@ -18,8 +18,7 @@ This rule checks if imported Glimmer components, helpers, or modifiers are marke
 | Helper / value mustache | `{{deprecatedHelper}}`                      |
 | Block component         | `{{#DeprecatedBlock}}…{{/DeprecatedBlock}}` |
 | Modifier                | `<div {{deprecatedModifier}}>`              |
-
-**Not covered:** `<MyComp @deprecatedArg={{x}}>` — checking argument deprecations is not yet implemented.
+| Component argument      | `<MyComp @deprecatedArg={{x}}>`             |
 
 ## Examples