refactor: enforce utility usage and centralize constants across all components

refactor: enforce utility usage and centralize constants across all components

- Replace .length/.size checks with isEmpty/isNotEmptyArray in 7 src/ files
- Replace Number.parseInt/parseFloat with convertToInt in OCPPServiceUtils
  (intentional fail-fast: malformed templates now throw instead of silent NaN)
- Keep Number.parseFloat in getLimitFromSampledValueTemplateCustomValue
  (NaN fallback contract requires it)
- Centralize route names (ROUTE_NAMES), placeholder (EMPTY_VALUE_PLACEHOLDER),
  and localStorage key in Vue UI (11 files)
- Extract 13 magic values to constants in Python ocpp-server
- Rename constants: WORKER_SET_VERSION, DEFAULT_RATE_WINDOW_MS, MS_PER_HOUR,
  DEFAULT_*_SECONDS in Python, DEFAULT_*_BYTES in UIServerSecurity