[CanReader]

• write a real crate page for docs.rs
• restructure the crate page around a tour
• add an architecture diagram to the crate page

What this changes

The docs.rs front page is now a tour. An architecture diagram sits under the intro, then Quick start with an examples table, then "A Tour of FastNN" with Models, Training, Data, Checkpoints, GPU, Generation and Debugging, then Tensors, Autograd, Feature flags, Platform support and Modules. Every snippet is a doctest. The tensor, autograd, nn, optim, data, serialize and cuda module pages get a front page with an example and a list of what lives there.

The diagram is assets/architecture.svg, referenced from lib.rs by its raw GitHub URL on master. It carries its own colours with a prefers-color-scheme rule, so it reads on both docs.rs themes.

Why

The docs.rs page was a tagline, one snippet and a list of module names, while the README explained far more. The front page is what people land on from crates.io, so it should explain how to use the library on its own.

How it was verified

• cargo test passes
• cargo clippy --all-targets -- -D warnings is clean
• Ran cuda_parity on a GPU
• Trained an example in --release
• No GPU here, CUDA side not runtime tested

Docs only. 41 doctests pass (up from 25) and cargo doc with -D warnings is clean, so every link resolves. Claims in the prose were checked against the code: unsafe only in src/cuda/, sm_75 to sm_90 from build.rs, the [1]-item batching rule, the load_training refusal. The SVG was checked under both colour schemes.

The image URL points at master, so it shows a broken image in a local cargo doc until this merges.

Checklist

• Every new or changed backward rule has a gradcheck case
• Every new kernel has a cuda_parity case
• tensor/ops and autograd/ops still mirror each other
• Public items have /// docs

About 300 public items (fields, variants, op methods) still have no doc comment. That is a separate pass.