Planet SymPy is now working again

[Aaron Meurer]

I recently did some updates to the Planet SymPy website
https://planet.sympy.org/. I completely rewrote the backend from
scratch and it's now much simpler and more modern. The website should
now be functional again. Let me know if you see any issues with the
site, and if you have any suggestions for further improvements. I did
the whole rewrite using Claude Code, which is pretty good at this sort
of thing, so further changes should be pretty simple to do.

GSoC students, please submit a pull request adding your blog RSS feed
(see https://github.com/sympy/planet-sympy/tree/main?tab=readme-ov-file#how-to-add-your-blog).
And if any SymPy developers have a blog that isn't included there
please feel free to add it as well.

Aaron Meurer