Flip fallback coverage model: each host defines its own recovery profile

Previously HOST1 defined what it would run for HOST2 (FALLBACK_HOST1_COVERS_HOST2_TIER*).
Now each host defines what it wants run when IT goes down (FALLBACK_HOST1_TIER*), and the
covering server reads the down host's conf via the RAM/persistent cache.

get_tier_containers() reads FALLBACK_${REMOTE_ID}_TIER* instead of
FALLBACK_${MY_ID}_COVERS_${REMOTE_ID}_TIER*. Tier data migrated to the correct host confs.
Writeback paths and delays were already REMOTE_ID-based — no change needed there.

Fallback/fallback.sh

@@ -75,10 +75,10 @@
 #   failed handback: containers stop on the covering server, remote goes down
 #   again mid-rsync. Strikes prevent this.
 #
-# MY_ID-Based Routing
-#   All tier arrays, DDNS lists, and writeback paths are selected via MY_ID
-#   set by detect_hosts() — not hostname string comparison. The same script
-#   and same config file handle both directions symmetrically.
+# REMOTE_ID-Based Coverage Config
+#   Tier arrays, writeback paths, and delays are all defined in the covered
+#   host's own conf and read via REMOTE_ID — not MY_ID. Each host owns its
+#   complete recovery profile. The same script handles both directions.
 #
 # ==============================================================================================
 # OPERATIONAL SAFEGUARDS
@@ -150,9 +150,10 @@
 #   FALLBACK_HOST*_STOP_ON_NO_NET
 #       Containers stopped when this host loses internet
 #
-#   FALLBACK_HOST*_COVERS_HOST*_TIER1–4
-#       Containers this host starts for the remote when remote is down, by tier.
-#       Variable pattern: FALLBACK_${MY_ID}_COVERS_${REMOTE_ID}_TIER${N}
+#   FALLBACK_HOST*_TIER1–4
+#       Containers started on this host when the partner is down — defined in the
+#       partner's own conf (what the partner wants covered). Read via REMOTE_ID.
+#       Variable pattern: FALLBACK_${REMOTE_ID}_TIER${N}
 #
 #   HOST*_TIER2_DELAY / TIER3_DELAY / TIER4_DELAY
 #       Minutes after FALLBACK entry before activating each tier.
@@ -537,8 +538,7 @@ remote_ddns_stop() {
 
 get_tier_containers() {
     local tier="$1"
-    local remote_id="${REMOTE_ID}"
-    local var_name="FALLBACK_${MY_ID}_COVERS_${remote_id}_TIER${tier}"
+    local var_name="FALLBACK_${REMOTE_ID}_TIER${tier}"
     eval "echo \"\${${var_name}[@]:-}\""
 }