feat: account for VM memory ballooning in host memory reporting (#1750)

* feat: account for VM memory ballooning in host memory reporting

Extend hostMemory.ts with a readBalloonedMemory() function that parses the
Balloon: field from /proc/meminfo, following the same fail-open pattern as
the ZFS ARC integration. When a nonzero balloon is detected, effective
memory fields (effectiveUsed, effectiveFree, effectiveUsagePercent) are
computed and exposed through /api/system/stats and /api/fleet/overview.

All consumers that derive meaning from host memory now prefer effective
values when present: the dashboard gauge, Fleet card RAM bar, mobile
views, health verdict, health status bar stat tile, and host RAM alerts.

Backward compatible: missing /proc/meminfo or absent Balloon: line
preserves exact current behavior. Old remote nodes without the new fields
continue rendering normally.

* refactor: extract shared helpers for balloon memory wiring

Extract readCandidateFile() and logSelectedPath() in hostMemory.ts to
deduplicate ARC and balloon file-read logic. Add memoryToWire() to
centralize the optional-field spread used by /api/system/stats and
/api/fleet/overview. Add getNodeMemUsed()/getNodeMemTotal() helpers
in nodeUtils.ts for frontend byte-text consumers.

* fix: make desktop fleet masthead aggregate balloon-aware

The desktop fleet overview's memory aggregate in useFleetOverview.ts still
summed raw memory.used, while the mobile fleet aggregate and per-node cards
already used effective values. Update to use getNodeMemUsed/getNodeMemTotal
helpers.

* fix: revert balloon adjustment from alerting and health decisions

Ballooned memory is host-reclaimed (unlike ZFS ARC, which the guest can
reclaim on demand). The guest cannot get ballooned pages back until the
hypervisor deflates them, so treating ballooned memory as available for
alerting or health can mask real memory pressure.

Keep balloon parsing, wire fields, and the dashboard context line as
informational-only. The memory gauge, health verdict, and host RAM alerts
now use the standard ARC-adjusted working-set percentage regardless of
balloon. Updated configuration.mdx and dashboard.mdx to document that
balloon data is informational and does not influence alerting.

docker-compose.yml

@@ -36,6 +36,8 @@ services:
       # available memory. Usually already visible in the container; only needed
       # if your runtime does not expose /proc/spl/kstat/zfs/arcstats.
       # - /proc/spl/kstat/zfs/arcstats:/host/proc/spl/kstat/zfs/arcstats:ro
+      # VM ballooning: mount /proc/meminfo if your runtime does not expose it.
+      # - /proc/meminfo:/host/proc/meminfo:ro
 
     environment:
       # ENVIRONMENT VARIABLES FOR INSIDE THE CONTAINER
@@ -50,6 +52,9 @@ services:
       # file, if it is not at a standard location. Leave empty to auto-detect
       # /host/proc/spl/kstat/zfs/arcstats then /proc/spl/kstat/zfs/arcstats.
       - SENCHO_ZFS_ARCSTATS_PATH=${SENCHO_ZFS_ARCSTATS_PATH:-}
+      # Optional: mount /proc/meminfo for VM memory ballooning awareness
+      # - /proc/meminfo:/host/proc/meminfo:ro
+      - SENCHO_PROC_MEMINFO_PATH=${SENCHO_PROC_MEMINFO_PATH:-}
     
     # ⚠️ GLOBAL ENVIRONMENT VARIABLES ⚠️
     # If your compose files rely on host-level shell variables (like $PUID, $TZ)