feat(race-day): start heats with an EFRA/IFMAR count-down and flying start

Race Day Start now runs a count-down (Go, 30 s - 5 min, default per
event) with calls every minute, 30 s and 10 s, grid call and 9..3
count for grid starts, hold/resume/+1 min/to 30 s/to 10 s/Go now, and
starts the heat by itself when it runs out. The transponder check runs
during the count-down, replacing the separate warm-up.

Adds a flying start mode (horn + clock is running, own clock per car)
as the qualifying default, and the latest personal clock start rules
from EFRA 9.3 / IFMAR 4.2.3 for flying and staggered starts.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "rc-racecore",
-  "version": "1.26.0",
+  "version": "1.27.0",
   "private": true,
   "description": "RC RaceCore live timing and race control with AMMC ingest and SQLite persistence",
   "engines": {