Replace VuePress with Zensical

[thunderbiscuit]

We've discussed migrating Zensical since we've been using it for the book of bdk. This PR will explore the viability of this migration.

Upside

• Much much faster builds
• Simpler setup (uv + Python versus Node/JS)

Downside

• Zensical doesn't currently offer a blog feature. This is not a big problem for us because (a) we don't actually host a very active blog (we retired it a while back) and the pages can simply be under an extra tab, and (b) they do plan on adding this feature to bring it up to parity with Material for MkDocs, which had a blog feature.

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[thunderbiscuit]

You can build the website locally like so:

gh pr checkout 263
uv sync
uv run zensical serve

[thunderbiscuit]

I have added the blog posts, and used the opportunity to do a major cleanup (which is up for discussion).

There were 47 blog posts. I propose to remove the following:

1. Call for Proposals: Full-Time Open Source Rust Maintainer
2. Security Advisory: Miniscript MINIMALIF Bug
3. Improving coin selection in BDK
4. Hidden Powers of Miniscript Policy & Descriptors
5. A Multisig between BDK and Core
6. Making Descriptor-based paper wallets
7. Using BDK with hardware wallets
8. Using BDK with Tor
9. Getting Started with rust-hwi
10. Fee estimation for light-clients (Part 1)
11. Fee estimation for light-clients (Part 2)
12. Fee estimation for light-clients (Part 3)
13. Spending Policy Decoded
14. BDK wallet with Bitcoin core RPC
15. BDK wallet as a BIP157 SPV light client
16. BDK-RN: Building React Native Apps with BDK
17. bdk-rn: Behind the scenes
18. BDK-FLUTTER: Building Flutter Apps with BDK
19. Command Line introduction to Bitcoin Wallet Development using bdk-cli
20. bdk-cli basics multi-sig 2 of 3 tutorial
21. Release v0.2.0
22. Release v0.3.0
23. Release v0.4.0
24. Release v0.5.0
25. Release v0.6.0
26. Release v0.7.0
27. Release v0.8.0
28. Release v0.9.0