Daemon-native worker registration

Preferred registration path for rensei-tui (`af`). Carries the `registrationToken` in the JSON body (not the `Authorization` header). Returns a `runtimeJwt` the daemon uses for all subsequent calls.

curl -X POST "https://example.com/v1/daemon/register" \  -H "Content-Type: application/json" \  -d '{    "registrationToken": "string",    "hostname": "string",    "maxAgents": 0  }'

{
  "workerId": "string",
  "runtimeJwt": "string",
  "heartbeatIntervalSeconds": 0,
  "pollIntervalSeconds": 0
}

{
  "error": "Session not found"
}

{
  "error": "Session not found"
}

{
  "error": "Session not found"
}