rename: failover → fallback throughout codebase — this system is Fallback, state is FALLBACK; preserve conventional failover comparisons

Monitors/README-Monitors.md

@@ -83,7 +83,7 @@ drive SMART attributes, ZFS pool state, ARC statistics, kernel memory pressure.
 Monitors/            ← observes and reports          (this folder)
 Docker_Essentials/   ← acts on containers            (docker_watchdog starts/stops)
 unRAID_Essentials/   ← acts on the server            (stability_watchdog, inotify_tuning)
-Fallback/            ← acts on the full stack        (failover, handback)
+Fallback/            ← acts on the full stack        (fallback, handback)
 Rsync/               ← calls bandwidth_monitor.sh    (auto-logs each sync)
 ```
 

Monitors/weekly_health_digest.sh

@@ -198,7 +198,7 @@ FINDINGS=()     # notable but not critical
 ISSUES=()       # need attention
 DIGEST_LINES=() # full report lines
 
-# ── Failover State ────────────────────────────────────────────────────────────────────────────
+# ── fallback State ────────────────────────────────────────────────────────────────────────────
 if [[ -f "$FALLBACK_STATE_FILE" ]]; then
     FALLBACK_STATE=$(grep "^state=" "$FALLBACK_STATE_FILE" 2>/dev/null | cut -d= -f2)
     if [[ -n "$FALLBACK_STATE" ]]; then