A consumer report on the GA pair: any minimal add/find/close script hangs
forever. Root cause was FOUR ref'd keep-alives brainy never released:
1+2. The global SIGTERM/SIGINT shutdown hooks (registered once at init) were
anonymous and never removed — a process.on signal listener holds a ref'd
signal handle. They are now named statics, deregistered when the LAST live
instance closes (Brainy.instances also stopped leaking closed instances);
a later init re-registers them.
3. UnifiedCache.startFairnessMonitor() created an interval it never stored,
cleared, or unref'd — unclearable by construction. Now stored + unref'd
(same posture as the existing memory-pressure timer): a cache monitor must
never keep the host process alive.
4. brainy.close() never called VirtualFileSystem.close(), stranding the VFS
background-maintenance interval and the PathResolver maintenance interval.
close() now shuts the VFS down.
Proof: a bare script (init/add/close, no process.exit) exits 1 ms after
close() returns; before the fix it hung until killed. 3 new lifecycle tests
pin the hook semantics (once globally, survive while other instances live,
removed on last close, re-register after).
