fix(api): retry commands that clash with a concurrent write

Services run commands through a CommandRunner that runs one again (up to
5 times, waiting a little longer each time) when its aggregate changed
underneath, e.g. a saga writing to the same ticket. Each command loads its
aggregate fresh and stores its events in one transaction, so a
ConcurrencyError means nothing was stored and running it again is safe.
People no longer get a 409 for it, and the e2e suite stops flaking.

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

libs/api/shared/application/src/index.ts

@@ -2,3 +2,4 @@ export * from './lib/ports/event-store';
 export * from './lib/aggregate-rehydrator';
 export * from './lib/shared.module';
 export * from './lib/event-recorder';
+export * from './lib/command-runner';