feat(backend): default verify_tls to false for lab/redteam Mythic

flip default to False at model, API fallback, adapter, and factory layers.
add migration 0008 flipping c2_config.verify_tls server_default to false.
suppress urllib3 InsecureRequestWarning when verify_tls is off.
adapt c2 tests to new verify_tls default.

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

backend/app/api/c2.py

@@ -84,7 +84,7 @@ def upsert_c2_config(eid: int):
     if not parsed.hostname:
         return jsonify({"error": "url must contain a hostname"}), 400
 
-    verify_tls = data.get("verify_tls", True)
+    verify_tls = data.get("verify_tls", False)
     if not isinstance(verify_tls, bool):
         return jsonify({"error": "verify_tls must be a boolean"}), 400