refactor: consolidate chat markdown rendering

apps/shared/ClawdbotKit/Tests/ClawdbotKitTests/ChatMarkdownPreprocessorTests.swift

@@ -0,0 +1,20 @@
+import Testing
+@testable import ClawdbotChatUI
+
+@Suite("ChatMarkdownPreprocessor")
+struct ChatMarkdownPreprocessorTests {
+    @Test func extractsDataURLImages() {
+        let base64 = "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVQIHWP4////GQAJ+wP/2hN8NwAAAABJRU5ErkJggg=="
+        let markdown = """
+        Hello
+
+        ![Pixel](data:image/png;base64,\(base64))
+        """
+
+        let result = ChatMarkdownPreprocessor.preprocess(markdown: markdown)
+
+        #expect(result.cleaned == "Hello")
+        #expect(result.images.count == 1)
+        #expect(result.images.first?.image != nil)
+    }
+}