[6.x] Keep the architectural background lines thin on wide screens

[jaygeorge]

The architectural lines background (e.g. on the Create Collection page) is stretched to the full width of the page, so the lines got thicker the wider the screen. We'd been dropping the opacity above 2000px to hide it, but that just made the lines fainter rather than thinner.

This adds vector-effect: non-scaling-stroke to the SVG's paths, so the lines stay 1px whatever the screen size. Two lines had a stroke-width of 1.49 that only came out at around 1px because their transform shrank them, so I've set those to 1.

With the lines no longer getting thicker, I've removed the opacity rule.

To test, open /cp/collections/create and resize the window from narrow to very wide. The lines should stay thin all the way.