nemora-postd: fix compile fail

host_manager.hpp is missing header for `std::thread`.

```
In file included from ../subprojects/nemora-postd/src/nemora.hpp:17,
                 from ../subprojects/nemora-postd/src/nemora.cpp:15:
../subprojects/nemora-postd/src/host_manager.hpp:76:26: error: ‘thread’ is not a member of ‘std’
   76 |     std::unique_ptr<std::thread> post_poller_;
```

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Icda54302f7770e5760dfa3c509c7086e47af75f9
diff --git a/subprojects/nemora-postd/src/host_manager.hpp b/subprojects/nemora-postd/src/host_manager.hpp
index 6ed2a33..8f1c7fd 100644
--- a/subprojects/nemora-postd/src/host_manager.hpp
+++ b/subprojects/nemora-postd/src/host_manager.hpp
@@ -22,6 +22,7 @@
 #include <mutex>
 #include <queue>
 #include <string>
+#include <thread>
 #include <unordered_map>
 #include <vector>