fix(hud): have game mode hand HUD its target ship instead of group lookup

HUDController found its ship via get_first_node_in_group("ship"), a group
that has 2+ members once a match has an AI opponent — it only worked
because the player ship happened to spawn first. spawn_camera_rig now
wires the HUD's ship the same way it already wires the camera rig's
target.

TODO.md

@@ -19,7 +19,7 @@ Bugs found in an adversarial review. None are gameplay- or physics-affecting, so
 - [ ] Goal scoring volume (3.5 x 1.5, `objects/goal.tscn`) is smaller than the drawn mouth (3.7 x 1.65, `ArenaBoundary.GOAL_APERTURE_*`) — a ball crossing the visible edge doesn't score. Derive the aperture constants from the goal's collision shape, the way `goal.gd:53` already measures its own visuals.
 - [x] `match_mode.gd`: full time can fire mid-kickoff-countdown, and the stalled coroutine resumes into the dying scene (can re-emit `kickoff_countdown` / unfreeze bodies for a frame). Guard `_run_kickoff_countdown` with a match-over flag.
 - [x] `match_mode.gd` emits `timer_updated` every frame for a value that changes once a second; the HUD re-formats and re-shapes the label each time. Emit only on change, matching `ship.gd`'s threshold-gated telemetry discipline.
-- [ ] `HUDController` binds to `get_first_node_in_group("ship")` in a group that always has 2+ members — works only because the player ship happens to spawn first. Have the game mode hand the HUD its target ship.
+- [x] `HUDController` binds to `get_first_node_in_group("ship")` in a group that always has 2+ members — works only because the player ship happens to spawn first. Have the game mode hand the HUD its target ship.
 - [ ] Reuse a member `ShipAction` in `ship.gd` (controllerless path) and `player_ship_controller.gd` instead of allocating one per physics tick; `ai_ship_controller.gd` already does this correctly.
 - [ ] Delete the duplicate 1 MB texture — `assets/textures/planet_surface.png` and `assets/models/nebula_planet_planet_surface.png` are byte-identical.