Animate repository cover

[0xprogrammable]

What changed

• add an animated version of the existing repository cover
• keep the Programmable mark static while the flower field moves in a seamless loop
• use the GIF at the top of the README

Verification

• 1774 × 887, 16 frames, 3.68-second infinite loop
• logo region is identical across every frame
• final GIF is 4.66 MB
• forge fmt --check
• forge build --sizes
• FOUNDRY_PROFILE=ci forge test (53 passed)

No contract source or deployment evidence changed.