Initial commit: Developer Tools MVP with visual editor

- Complete React app with 7 developer tools
- JSON Tool with visual structured editor
- Serialize Tool with visual structured editor
- URL, Base64, CSV/JSON, Beautifier, Diff tools
- Responsive navigation with dropdown menu
- Dark/light mode toggle
- Mobile-responsive design with sticky header
- All tools working with copy/paste functionality

node_modules/eslint-plugin-jest/docs/rules/no-interpolation-in-snapshots.md

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+# Disallow string interpolation inside snapshots (`no-interpolation-in-snapshots`)
+
+Prevents the use of string interpolations in snapshots.
+
+## Rule Details
+
+Interpolation prevents snapshots from being updated. Instead, properties should
+be overloaded with a matcher by using
+[property matchers](https://jestjs.io/docs/en/snapshot-testing#property-matchers).
+
+Examples of **incorrect** code for this rule:
+
+```js
+expect(something).toMatchInlineSnapshot(
+  `Object {
+    property: ${interpolated}
+  }`,
+);
+
+expect(something).toMatchInlineSnapshot(
+  { other: expect.any(Number) },
+  `Object {
+    other: Any<Number>,
+    property: ${interpolated}
+  }`,
+);
+
+expect(errorThrowingFunction).toThrowErrorMatchingInlineSnapshot(
+  `${interpolated}`,
+);
+```
+
+Examples of **correct** code for this rule:
+
+```js
+expect(something).toMatchInlineSnapshot();
+
+expect(something).toMatchInlineSnapshot(
+  `Object {
+    property: 1
+  }`,
+);
+
+expect(something).toMatchInlineSnapshot(
+  { property: expect.any(Date) },
+  `Object {
+    property: Any<Date>
+  }`,
+);
+
+expect(errorThrowingFunction).toThrowErrorMatchingInlineSnapshot();
+
+expect(errorThrowingFunction).toThrowErrorMatchingInlineSnapshot(
+  `Error Message`,
+);
+```
+
+## When Not To Use It
+
+Don't use this rule on non-jest test files.