Dir-sync first send waits behind another writer's lock and records more detail

When directory sync (the feature that copies your files through git) sends for the first time, it may find that another process on the same machine holds a lock, meaning that process is writing. Before, this counted as a failure. Now sync waits for the lock to clear. If the writer is on a different machine, sync stops waiting. Other changes:

• The step that captures the current state can now report kept_here with reasons such as local_failures, or failed with uploads_failing.
• The usage event tengu_dir_sync_git_capture_point gains a reason field, and the first-send data records writer_elsewhere and lock_waited.
• A new install_ack trigger sends an update after incoming changes are applied.
• The stopped state now reports whether the first upload happened.
• Some waiting messages were reworded, for example "your message goes as soon as that clears."