As you say drapes with linings are going to be heavy so you wouldn't be able to use tension rods. How about having a multiple panel screen thingy made that is portable and folds up. I just can't think what they are called now. But basically you would spread the panels across at night for coverage of the window/s and fold them up in the morning. I hope you know what I mean. Perhaps also have castors at the bottom of the panel screen thingy to easily move it wherever you want to.

Drilling into a "post tensioned" concrete can have amazingly destructive results if you nick one of the cables that is in there ... it explodes!

Can you use tension rods to hold sheers?

Make a frame that wedges between floor and ceiling to hold the hardware (frame the windows with 2x2s, hang drapes on there).

Give up on the drapes and enjoy the view, except for a few screens for critical privacy?

Do you have a normal sheet rocked ceiling?
Drill there, that's unconventional

lazygardens has good ideas-

I've done the 'frame' a few times, and it works out very nicely- actually, I've done it with salvaged bamboo, and it even looked stylish.

folding screens can be a nice alternative, they create the look of a transom window above the screen.

the stained glass film is another option- it comes in a number of looks from frosted to cathedral window, goes on quickly and easily, comes off just as easily, and doesn't hurt anything.

maybe look into light blocking honeycomb shades which should be lighter than drapes.

I would get in touch with your local authorities (sorry, have no idea what they're called there) regarding being able to expect reasonable facilities for living, the same way as you would if there was no heat or hot water, etc. You must allow people to have privacy and protection from light, and not tell them they have to come up with unconventional methods to hang drapes, etc. This is nonsense and I wouldn't put up with it for 5 minutes.

You can buy a separate blackout lining for drapes. If you got those, along with unlined drapes, could you use two tension rods, one behind the other, with the lining hanging behind the drapes?

Or maybe use the shower curtain tension rods--they seem to be a bit sturdier than the regular kind.

Is there nothing on the windows? I've rented a few places where I wasn't allowed to use nails or screws to hang curtain rods, but there was always a landlord-provided blind or shade in place. The landlord never presented me with bare windows and an order to come up with an unconventional method of covering the windows.