It’s so flimsy,” I thought as the Gemini astronauts in “First Man” were squeezed into a thimble-sized space capsule sitting on a rocket — their only protection as they are hurled 230,000 miles into the void of space.As the men were inserted into the claustrophobic chamber, I flashed back to the scene in “The Wizard of Oz” where the charlatan wizard unhinges a door cut into the tin …