Fixes the incorrect DefaultData reuse of Player::MessageHandlers -- BTPlayer now
has its own handler table (DropZoneReply, VehicleDead, Score, ScoreInflicted,
ScoreUpdate; the last two add BT message IDs) chained onto the base set, matching
the .data table recovered in BT411. A mission-start DropZoneReply now routes to
BTPlayer::DropZoneReplyMessageHandler (the real spawn/respawn dispatch skeleton)
instead of the base "should not be handled by base player class" Fail stub.
Boot ladder now runs the full engine + app + network + mission + player path and
reaches the spawn handshake, halting at CreatePlayerVehicle -> Mech::Make -- the
Mech subsystem frontier (Mech ctor + mech2/3/4 + subsystems + weapons), the next
major reconstruction milestone. Scoring/death handlers, PlayerSimulation, and the
mech-placement tail staged with documented Fail bodies (BTPLAYER.NOTES.md).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>