NewServer launches the SyncFileBrowserMounts goroutine (reads integrationMgr)
from the constructor, BEFORE main.go's SetIntegrationManager write — so the
init-only happens-before that covers the other Set* fields does NOT hold here,
making it a genuine data race (handlers.go:358/360/1433 reads vs server.go:162
write). Converted the field to atomic.Pointer[integrations.Manager]; setter
Stores, all 3 readers Load(). Regression test reproduces the concurrent access
(clean under -race; flags on the pre-fix plain-pointer field).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
