feat: enhance Claude Code client detection with similarity matching

- Add string-similarity library for robust prompt comparison
- Extract Claude Code system prompts to separate contents module
- Implement similarity-based validation with configurable thresholds
- Support different validation logic for Haiku vs other Claude models
- Fix validation to properly handle array format system prompts

🤖 Generated with [Claude Code](https://claude.ai/code)

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

src/utils/text-similarity.js

@@ -0,0 +1,18 @@
+import stringSimilarity from 'string-similarity'
+
+function normalize(value) {
+  return value.replace(/\s+/g, ' ').trim()
+}
+
+export function simple(actual, expected, threshold) {
+  if (typeof expected !== 'string' || !expected.trim()) {
+    throw new Error('Expected prompt text must be a non-empty string')
+  }
+
+  if (typeof actual !== 'string' || !actual.trim()) {
+    return { score: 0, threshold, passed: false }
+  }
+
+  const score = stringSimilarity.compareTwoStrings(normalize(actual), normalize(expected))
+  return { score, threshold, passed: score >= threshold }
+}