When HindsightEmbedded(profile="myapp") starts a daemon, the profile
was never written to metadata.json or given a .env file, making it
invisible to `hindsight-embed profile list` and other CLI commands.
Add _register_profile() to DaemonEmbedManager which saves HINDSIGHT_API_*
config to ~/.hindsight/profiles/{name}.env and registers the port in
metadata.json. Called after a successful new daemon start and when the
daemon is already running, so orphaned profiles also get registered on
next use.