meta(docs): clean up developer documentation

## context

the workspace changed quite a bit since #13880 was opened. `wallets` moved to `foundry-core`, `solar` and `tui` were added, and there are more crates under `evm/`. manually documenting every crate and its dependencies in one file will probably become outdated again pretty quickly.

as @zerosnacks mentioned in https://github.com/foundry-rs/foundry/issues/13880#issuecomment-4161052129, i think it is higher leverage to remove this page and improve the generated crate docs and the book incrementally.

there are a few other things to clean up at the same time:

- `docs/dev/README.md` is linked as the developer guidelines, but it still says that it is incomplete and possibly outdated;
- the index does not include existing pages like `lintrules.md`, `output-channels.md`, and `showmap.md`;
- it is not very clear what should live in `docs/dev`, Rustdoc, the book, `CONTRIBUTING.md`, or `AGENTS.md`;
- some instructions are duplicated between these places and can drift;
- crate-level Rustdoc exists for the whole workspace, but some crate landing pages still have very little context.

i think the split should roughly be:

- user-facing guides, config and CLI documentation belong in the [book](https://getfoundry.sh/);
- crate/module internals and APIs belong in the source as Rustdoc and are published at https://foundry-rs.github.io/foundry/;
- cross-crate contributor workflows and invariants can stay in `docs/dev` or `CONTRIBUTING.md`;
- agent-specific instructions should stay in `AGENTS.md`, but link to the canonical docs instead of duplicating them;
- release-facing changes should use `.changelog` and the generated changelog/release notes.

## work

- [x] remove `docs/dev/architecture.md` and its entry from the developer docs index;
- [x] clean up `docs/dev/README.md` and make it an accurate index of the contributor documentation we actually maintain;
- [x] audit the existing `docs/dev/*.md` files and decide which ones should stay, be updated, move somewhere else, or be removed;
- [x] link the developer docs to the book, generated Rustdoc, `CONTRIBUTING.md`, and the changelog instructions;
- [x] reduce duplicated guidance between `docs/dev`, `CONTRIBUTING.md`, and `AGENTS.md`;
- [x] improve crate-level Rustdoc overviews incrementally where they are missing useful context;
- [x] open focused issues in `foundry-rs/book` for concrete user-facing gaps instead of tracking a general book rewrite here;
- [x] close #13880 as superseded by this issue.

i don't think we should remove all of `docs/dev`. pages like `cheatcodes.md`, `output-channels.md`, and `showmap.md` are still actively maintained. the goal is mostly to remove the stale parts and make the ownership of the remaining docs clearer.