Fix WARDOGS kill requests requiring a JSON body

[speccycy]

Summary

WARDOGS now rejects POST /v1/players/{id}/kill when the request has no body.

Observed on a live server:

POST /v1/players/{id}/kill
(no body)
-> 501 unsupported_transfer_encoding
-> "The request could not be parsed."

Sending an empty JSON object succeeds:

POST /v1/players/{id}/kill
Content-Type: application/json

{}
-> 200 OK

This PR sends {} for both kill call sites:

• the regular Kill action, which is also used by AFK protection and rule kills
• the respawn kill after changeTeam

It also adds regression tests that assert the empty JSON body is sent.

Why

Without this, manual Kill fails and AFK protection rounds fail with:

The request could not be parsed.

on current WARDOGS builds.

Validation

Live RCON validation:

• no body: 501 unsupported_transfer_encoding
• {} body: 200 OK
• player was killed successfully