feat(raft-adapter-conformance): send explicit reply on every config-push outcome

handle_repl_config_push now sends a ReplConfigPushReply{accepted,term}
from every exit path instead of silently dropping on the four reject
conditions (malformed request, missing bytes/sha256, sha256 mismatch,
conf_save_config failure). Term is sourced live from c->ha.term.
-EAGAIN activation-defer still replies accepted=1, unchanged.

Adds an XCE_TESTING-only send-hook mirroring ha_wal_ack_send_hook so
tests can observe the reply payload without a live endpoint.

src/controller/config_repl.h

@@ -463,6 +463,19 @@ int load_primary_config_for_test(cluster_t *c);
  */
 extern void (*load_primary_config_race_hook)(void);
 
+/*
+ * config_push_reply_send_hook: test-only injection point for the outbound
+ * ReplConfigPushReply built by send_config_push_reply() (config_repl.c).
+ * When non-NULL, called with (term, version_tag, accepted) INSTEAD of
+ * building/sending the real reply over ep -- lets a unit test observe a
+ * config-push accept OR reject reply without a live endpoint
+ * (raft-adapter-conformance task 2.1, mirrors ha_wal_ack_send_hook /
+ * bug-1479). NULL in production. Set by test infrastructure
+ * (test_config_repl.c) before the relevant tests run.
+ */
+extern void (*config_push_reply_send_hook)(uint64_t term, uint64_t version_tag,
+                                            int accepted);
+
 /*
  * push_ctx_t: exposed under XCE_TESTING so unit tests can construct
  * synthetic push contexts to drive wait_all_with_timeout_for_test().