feat(filters): Add base64_encode and base64_decode filters for Shopify compatibility (#828)

* feat(filters): add base64 encode and decode

* fix: use Object.defineProperty for cross-platform btoa/atob mocking

* docs(filters): update docs

* docs(filters): update version

test/integration/filters/base64.spec.ts

@@ -0,0 +1,78 @@
+import { test } from '../../stub/render'
+
+describe('filters/base64', function () {
+  describe('base64_encode', function () {
+    it('should encode a simple string', () => {
+      return test('{{ "one two three" | base64_encode }}', 'b25lIHR3byB0aHJlZQ==')
+    })
+
+    it('should encode an empty string', () => {
+      return test('{{ "" | base64_encode }}', '')
+    })
+
+    it('should encode a string with special characters', () => {
+      return test('{{ "Hello, World! @#$%" | base64_encode }}', 'SGVsbG8sIFdvcmxkISBAIyQl')
+    })
+
+    it('should encode unicode characters', () => {
+      return test('{{ "你好世界" | base64_encode }}', '5L2g5aW95LiW55WM')
+    })
+
+    it('should handle undefined input', () => {
+      return test('{{ foo | base64_encode }}', '')
+    })
+
+    it('should handle null input', () => {
+      return test('{{ null | base64_encode }}', '')
+    })
+
+    it('should handle numeric input', () => {
+      return test('{{ 123 | base64_encode }}', 'MTIz')
+    })
+
+    it('should handle boolean input', () => {
+      return test('{{ true | base64_encode }}', 'dHJ1ZQ==')
+    })
+  })
+
+  describe('base64_decode', function () {
+    it('should decode a simple string', () => {
+      return test('{{ "b25lIHR3byB0aHJlZQ==" | base64_decode }}', 'one two three')
+    })
+
+    it('should decode an empty string', () => {
+      return test('{{ "" | base64_decode }}', '')
+    })
+
+    it('should decode a string with special characters', () => {
+      return test('{{ "SGVsbG8sIFdvcmxkISBAIyQl" | base64_decode }}', 'Hello, World! @#$%')
+    })
+
+    it('should handle undefined input', () => {
+      return test('{{ foo | base64_decode }}', '')
+    })
+
+    it('should handle null input', () => {
+      return test('{{ null | base64_decode }}', '')
+    })
+
+    it('should handle numeric input', () => {
+      return test('{{ "MTIz" | base64_decode }}', '123')
+    })
+
+    it('should handle boolean input', () => {
+      return test('{{ "dHJ1ZQ==" | base64_decode }}', 'true')
+    })
+  })
+
+  describe('base64 round-trip', function () {
+    it('should encode and decode back to original', () => {
+      return test('{{ "Hello, World!" | base64_encode | base64_decode }}', 'Hello, World!')
+    })
+
+    it('should handle complex strings', () => {
+      const complexString = 'Special chars: !@#$%^&*()_+-=[]{}|;:,.<>?'
+      return test(`{{ "${complexString}" | base64_encode | base64_decode }}`, complexString)
+    })
+  })
+})