Suggestion: Rename documentation title to "The Just Book"

### Description

Currently, the title of the just documentation is **"Just Programmer's Manual"**. Given that just is heavily integrated into the Rust ecosystem, adopting the widely accepted Rust documentation naming convention—**"The [Project] Book"**—would bring better brand consistency and familiarity to users.

### Examples in the Ecosystem

Many official and prominent Rust tools/projects use this naming convention:

* **The Cargo Book**: https://doc.rust-lang.org/cargo/
* **The Rustdoc Book**: https://doc.rust-lang.org/rustdoc/
* **The Rustup Book**: https://doc.rust-lang.org/rustup/
* **The Rhai Book**: https://rhai.rs/book/
* **The Cairo Book**: https://www.starknet.io/cairo-book/

### Proposed Changes

Update from **"Just Programmer's Manual"** to **"The Just Book"**.

Search the documentation source for the title "Just Programmer's Manual" and inspect how the documentation title is defined. Rename it to "The Just Book", then verify that the generated or published documentation shows the new title consistently.

Written by the indexing model from the issue text.