feat(race): synchronized countdown start and live position/timer HUD

Description

All players in a Race Mode session must start simultaneously via a shared 3-2-1-GO countdown. Movement and ring collision are suppressed before the GO signal. The HUD gains a live elapsed-timer action bar and a race position display.

Acceptance Criteria

• A 3-2-1-GO countdown is broadcast to all players in the lobby phase before map start
• Player movement and elytra launch are blocked until the GO signal fires
• Ring collision events are ignored until the GO signal fires
• After GO, an elapsed timer displays in the action bar (format: `MM:SS.ms` or `SS.ms`)
• A race position display shows each player's current place (e.g. `1 / 4`) and gap to the leader
• `HudComponent` is extended to carry timer and position state
• Countdown is implemented in `MinestomLobbyPhase` or a dedicated `CountdownPhase`
• Timer starts at the exact tick the GO signal fires (consistent across all players)
• Unit tests cover countdown sequence and freeze/unfreeze transitions
• Minestom testing framework used for phase-level tests

Technical Details

• The freeze mechanic must not interfere with camera movement (look direction remains free)
• Position ranking is recomputed every tick based on rings completed, then elapsed time as tiebreaker
• `HudComponent` is a Java record; use a builder or `with*()` pattern for updates
• The GO signal is a server-side event dispatched via the phase system, not a client packet race

Dependencies

• #168 (time-bracket scoring — timer must align with the same start tick used for scoring)

Estimate

M

Start with MinestomLobbyPhase, the possible dedicated CountdownPhase, and the HudComponent record; review dependency #168 to align the shared start tick. Use the Minestom testing framework for phase-level tests covering the countdown and freeze/unfreeze transitions, and verify the timer, position, gap, and movement behavior against the acceptance criteria.