Add staggered-start car call-outs and a per-driver done indicator

Staggered-start qualifying heats now announce each car's transponder
number in grid order (~3s apart) right after the official start,
matching what a track announcer does when releasing cars one at a
time; mass/position starts are unaffected. The Timing leaderboard and
every overlay variant now also show a green "Done" flag next to a
driver's name once their own personal timing window (which already
started at their own first crossing) has elapsed, even while the
session is still running for other drivers.

Also confirmed two things already worked correctly: finals already
always start everyone together with the shared countdown/lights/tone
sequence, and practice's time-up announcement already says "finish
the lap you are on" - only a "2 minutes remaining" cue is genuinely
missing from the existing 1min/30s/10s ladder, left as an open
question for the user.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

rc-race-sound-pack/sound_manifest.json

@@ -46,6 +46,7 @@
       "grid_open": "The starting grid is open.", "grid_closed": "The starting grid is closed.",
       "race_1_minute": "Race starts in one minute.", "race_30_seconds": "Thirty seconds to start.", "race_10_seconds": "Ten seconds to start.",
       "drivers_ready": "Drivers, stand by.", "start_sequence": "Starting on the sound of the tone.", "false_start": "False start.", "restart_race": "Prepare to restart the race.",
+      "staggered_release": "Car {tp}.",
       "personal_best": "Personal best. {driverName}. {lapTime}.", "fastest_lap": "Fastest lap. {driverName}. {lapTime}.",
       "training_stable_pace": "{driverName}, good pace and consistent driving.",
       "track_record": "New track record. {driverName}. {lapTime}.", "new_leader": "New race leader. {driverName}.",
@@ -67,6 +68,7 @@
       "grid_open": "Startfältet är öppet.", "grid_closed": "Startfältet är stängt.",
       "race_1_minute": "Start om en minut.", "race_30_seconds": "Trettio sekunder till start.", "race_10_seconds": "Tio sekunder till start.",
       "drivers_ready": "Förare, gör er redo.", "start_sequence": "Start på signalen.", "false_start": "Felaktig start.", "restart_race": "Förbered omstart.",
+      "staggered_release": "Bil {tp}.",
       "personal_best": "Personbästa. {driverName}. {lapTime}.", "fastest_lap": "Snabbaste varv. {driverName}. {lapTime}.",
       "training_stable_pace": "{driverName}, bra tempo och stabil körning.",
       "track_record": "Nytt banrekord. {driverName}. {lapTime}.", "new_leader": "Ny ledare. {driverName}.",