edge-host: fix settings-backup terminator check (trailing newline)

The zwave-js settings backup guard in #120 checked `tail -c1 == "}"`, but
settings.json ends with "}\n" — so the last byte is a newline and the guard
always skipped ("not }-terminated"), producing no backup. Strip trailing
whitespace before the check so a valid, newline-terminated file is backed up
while a genuinely truncated one is still rejected.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

ansible/roles/edge-host/templates/edge-zwave-settings-backup.j2

@@ -11,8 +11,9 @@ bak="$src.bak"
 
 # Only back up a plausibly-intact file: non-empty and JSON-object-terminated.
 # This avoids overwriting a good backup with a truncated (mid-write) file.
+# Ignore trailing whitespace — settings.json ends with "}\n".
 [ -s "$src" ] || { echo "settings.json missing/empty — skip"; exit 0; }
-[ "$(tail -c1 "$src")" = "}" ] || { echo "settings.json not }-terminated (mid-write?) — skip"; exit 0; }
+[ "$(tail -c 64 "$src" | tr -d '[:space:]' | tail -c1)" = "}" ] || { echo "settings.json not }-terminated (mid-write?) — skip"; exit 0; }
 
 # Skip if unchanged since the last backup.
 if [ -f "$bak" ] && cmp -s "$src" "$bak"; then