Fix Team Race duplicate-membership bug and two related team-roster gaps

Reported by the user: creating a team, adding the wrong driver, then
moving that driver to another team by ticking them on the new team's
edit form left the driver on both teams at once. Root cause: there
was never a "move" action - the edit form only ever added a driver to
the team being saved, never removed them from wherever they already
were. Live laps from a driver on two teams were then silently
credited to only the first-matching team, with no clear error.

reassignTeamMembers (event_race_logic.js) now strips a driver/car
being saved onto one team out of every other team in the same event,
and the team checkbox list shows which team a driver is already on
before you move them.

Also fixed two related gaps found while investigating, at the user's
request to fix everything: getTeamDriverPool had regressed to
ignoring the event's class/participant scoping entirely (showing
every driver in the club), and deleting a driver or car left them
behind in team rosters forever. Added a duplicate_team_members Race
Day preflight check as defense in depth for any already-corrupted
saved state.

Verified with new unit tests for reassignTeamMembers, getTeamDriverPool
and the new preflight check, plus a new permanent browser test
reproducing the user's exact reported scenario end to end.

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

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "rc-racecore",
-  "version": "1.10.1",
+  "version": "1.10.2",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "rc-racecore",
-      "version": "1.10.1",
+      "version": "1.10.2",
       "hasInstallScript": true,
       "dependencies": {
         "better-sqlite3": "^12.11.1",