incremental-sync.ts and api/cw/sync.ts imported getBoss() from workert.ts.
When workert.ts (the entry point) dynamically imported incremental-sync.ts,
it triggered a circular module re-evaluation that hung indefinitely.
Extract the PgBoss singleton and getBoss() factory to a new boss-instance.ts
module that neither has top-level async side-effects nor imports from
workert.ts. All consumers (workert.ts, index.ts, incremental-sync.ts,
cw/sync.ts) now import from boss-instance.ts instead.
