Add ast-grep rule to prevent String() function usage

Prefer .toString() or .toLocaleString() over String() for
more predictable behavior and consistency.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.ast-grep/rule-tests/__snapshots__/no-string-function-snapshot.yml

@@ -0,0 +1,20 @@
+id: no-string-function
+snapshots:
+  String(123):
+    labels:
+    - source: String(123)
+      style: primary
+      start: 0
+      end: 11
+  String(Date.now()):
+    labels:
+    - source: String(Date.now())
+      style: primary
+      start: 0
+      end: 18
+  String(value):
+    labels:
+    - source: String(value)
+      style: primary
+      start: 0
+      end: 13

.ast-grep/rule-tests/no-string-function-test.yml

@@ -0,0 +1,13 @@
+id: no-string-function
+valid:
+  # toString() is fine
+  - value.toString()
+  - (123).toString()
+  - date.toLocaleString()
+  # Other functions named String are fine
+  - myString(value)
+invalid:
+  # String() function should be flagged
+  - String(value)
+  - String(123)
+  - String(Date.now())

.ast-grep/rules/no-string-function.yml

@@ -0,0 +1,7 @@
+id: no-string-function
+language: typescript
+severity: error
+message: "Don't use String() - use .toString() or .toLocaleString() instead."
+note: "String() can have unexpected behavior. Use .toString() for general conversion or .toLocaleString() for locale-aware formatting."
+rule:
+  pattern: String($VAL)