Two platform-wide production fixes for consumers on bare VMs / mmap-filesystem storage.
BUG A — auto maxQueryLimit collapsed to ~1000 on healthy VMs → 500s on legitimate
queries. getAvailableMemory() read os.freemem() (kernel MemFree, which excludes
reclaimable page cache and reads as tens of MB on a page-cache-heavy mmap box).
Now reads /proc/meminfo MemAvailable (the `free -h` figure), falling back to
os.freemem() only off-Linux; auto-detected caps (container/free branches) are floored
at 10k so a misread can't collapse them. Explicit maxQueryLimit/reservedQueryMemory
are honored as-is.
BUG B — native mmap vector fast-path never engaged (per-entity reads → 57s cold start
on a 283MB brain). FileSystemStorage now exposes a public `rootDirectory` getter; the
native vector provider feature-detects it to enable its memory-mapped graph path.
brainy stored it as the protected `rootDir`, so the gate silently failed. Self-heals
after the first post-upgrade flush writes the mmap file.
Regression tests: auto-cap floor (container/free/explicit-override) + the rootDirectory
getter. Build clean; full suite 1483 green.
