refactor: replace 54 unsafe error casts with instanceof guards

refactor: replace 54 unsafe error casts with instanceof guards

All 'error as Error', 'error as OCPPError', and 'error as
NodeJS.ErrnoException' casts replaced with proper instanceof
type narrowing across 16 files. Uses the pattern already
established in the auth strategies module:
  error instanceof Error ? error.message : String(error)

For call sites that pass error objects to functions, wraps
non-Error values: error instanceof Error ? error : new Error(String(error))