feat: rename kill to destroy, improve code interpreter, update README

- Rename Capsule.kill/AsyncCapsule.kill to destroy for frontend consistency
- Add Sandbox deprecation alias to wrenn.code_interpreter module
- run_code text falls back to stripped stdout when no expression result
- Strip quotes from string expression results (matching e2b behavior)
- _ensure_kernel reuses existing Jupyter kernels before creating new ones
- Rewrite README with complete examples for capsules and code interpreter
- Remove stale AGENTS.md

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_capsule_features.py

@@ -68,9 +68,9 @@ class TestCapsuleCreate:
 
 class TestCapsuleStaticMethods:
     @respx.mock
-    def test_static_kill(self):
+    def test_static_destroy(self):
         route = respx.delete(f"{BASE}/v1/capsules/cl-1").respond(204)
-        Capsule._static_kill("cl-1", api_key="wrn_test1234567890abcdef12345678")
+        Capsule._static_destroy("cl-1", api_key="wrn_test1234567890abcdef12345678")
         assert route.called
 
     @respx.mock