Fix dead/incorrect vars and consolidate duplicated logic into common.sh

Codebase-wide audit pass: fixed real bugs (SSH hangs missing BatchMode,
local-outside-function no-ops, variable name collisions, a truncated
ratio calc, wrong state-dir path, DARK vs NO_INTERNET drift, and more),
then pulled logic that was duplicated across multiple scripts — arr
cleanup safety gates, docker restart ordering, container maintenance
stop/restart, watchdog state-file helpers, partnership role resolution,
cert expiry checks, remote node discovery, and TMDB discovery scoring —
into common.sh so each now has a single implementation.

Monitors/weekly_health_digest.sh

@@ -270,7 +270,7 @@ fi
 # ── Transcode Ramdisk ─────────────────────────────────────────────────────────────────────────
 if mountpoint -q "$RAMDISK_PATH" 2>/dev/null; then
     RAMDISK_USED_KB=$(df "$RAMDISK_PATH" --output=used 2>/dev/null | tail -1 | tr -d ' ')
-    RAMDISK_USED_GB=$(awk "BEGIN {printf \"%.2f\", ${RAMDISK_USED_KB:-0} / 1048576}")
+    RAMDISK_USED_GB=$(kb_to_gb "$RAMDISK_USED_KB")
     SYMLINK_TARGET=$(readlink "$TRANSCODE_LINK" 2>/dev/null || echo "unknown")
     DIGEST_LINES+=("$ICON_RAM Transcodes: ${RAMDISK_USED_GB}GB used → $SYMLINK_TARGET")
 
@@ -309,7 +309,7 @@ if [[ -f "${BANDWIDTH_LOG:-}" ]] && [[ -s "$BANDWIDTH_LOG" ]]; then
     YESTERDAY=$(date -d "yesterday" '+%Y-%m-%d')
     YESTERDAY_BYTES=$(awk -F'|' -v d="$YESTERDAY" '$1==d{sum+=$6} END{print sum+0}' \
         "$BANDWIDTH_LOG")
-    YESTERDAY_GB=$(awk "BEGIN {printf \"%.2f\", ${YESTERDAY_BYTES:-0} / 1073741824}")
+    YESTERDAY_GB=$(bytes_to_gb "$YESTERDAY_BYTES")
     YESTERDAY_LARGE=$(awk -F'|' -v d="$YESTERDAY" '$1==d && $7=="LARGE"' \
         "$BANDWIDTH_LOG" | wc -l)
 
@@ -329,12 +329,8 @@ if [[ ${#CERT_MONITOR_DOMAINS[@]} -gt 0 ]] && command -v openssl >/dev/null 2>&1
     CERT_ISSUES=()
     for domain in "${CERT_MONITOR_DOMAINS[@]}"; do
         [[ -z "$domain" ]] && continue
-        expiry_str=$(echo | timeout "${CERT_TIMEOUT:-10}" openssl s_client \
-            -connect "${domain}:443" -servername "$domain" \
-            2>/dev/null | openssl x509 -noout -enddate 2>/dev/null | cut -d= -f2)
-        if [[ -n "$expiry_str" ]]; then
-            expiry_epoch=$(date -d "$expiry_str" +%s 2>/dev/null)
-            days_remaining=$(( (expiry_epoch - $(date +%s)) / 86400 ))
+        if check_cert_expiry "$domain" 443 "${CERT_TIMEOUT:-10}"; then
+            days_remaining="$_CERT_DAYS"
             if [[ "$days_remaining" -le "${CERT_CRIT_DAYS:-7}" ]]; then
                 CERT_ISSUES+=("$domain: ${days_remaining}d CRITICAL")
                 SHOULD_SEND=true