fix(search): tighten mock type cast for better type safety

Replace `as any` cast with `as unknown as ReturnType<typeof createMeiliClient>`
in the mock client factory. This preserves type safety without requiring the mock
to implement the full SDK interface.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/settings.local.json

@@ -69,7 +69,11 @@
       "Bash(npx jest *)",
       "Bash(pnpm --filter @tower/worker test -- --testPathPattern=forward)",
       "Bash(pnpm --filter @tower/worker test -- forward.processor.test.ts)",
-      "Bash(npm test *)"
+      "Bash(npm test *)",
+      "Bash(grep -v \"^$\")",
+      "Bash(npm info *)",
+      "Bash(pnpm --filter @tower/search test)",
+      "Bash(pnpm --filter @tower/search build)"
     ]
   }
 }