Automerge-C API Docs

I was talking to @jkankiewicz about getting the generated [Automerge-C](https://github.com/automerge/automerge/tree/main/rust/automerge-c) docs hosted and linked from the site.

To build the docs:
```
cmake -E make_directory automerge-c/build
cmake -S automerge-c -B automerge-c/build
cmake --build automerge-c/build --target automerge_docs
cmake -E copy_directory automerge-c/build/docs/html /automerge-c
```

The docs end up at `/automerge-c/index.html`

They're versioned along with the rest of the repo, so adding a step to generate and upload (to gh-pages) these docs as part of the JS or rust release workflow perhaps makes sense. (Will need to talk to @alexjg about this.) Worth noting — the JS docs are hosted on GH Pages, but I think the rust docs are hosted elsewhere, so we might *need* to build them as part of the JS release process (because all GH Pages stuff seemingly needs to be uploaded together).

Here's a sketch GPT generated:

```
publish-js-docs:
runs-on: ubuntu-latest
if: "!github.event.release.prerelease"
defaults:
run:
working-directory: ./javascript
steps:
- uses: actions/checkout@v5
- uses: actions/setup-node@v5
with:
node-version: "20.x"
registry-url: "https://registry.npmjs.org"
- name: Install wasm-bindgen-cli
run: cargo install wasm-bindgen-cli wasm-opt
- name: Install wasm32 target
working-directory: rust
run: rustup target add wasm32-unknown-unknown
- name: yarn install
run: yarn install
- name: build js
run: node ./scripts/build.mjs
- name: build js docs
run: npx typedoc --out api-docs/js

# 👇 Added C docs build
- name: Set up CMake
uses: jwlawson/actions-setup-cmake@v2

- name: Build C docs
run: |
cmake -E make_directory automerge-c/build
cmake -S automerge-c -B automerge-c/build
cmake --build automerge-c/build --target automerge_docs
mkdir -p api-docs/c
cp -r automerge-c/build/docs/* api-docs/c || true

- name: Deploy 🚀
uses: JamesIves/github-pages-deploy-action@v4
with:
branch: gh-pages
folder: ./javascript/api-docs
target-folder: api-docs
```

Which should put the docs here:

* `/api-docs/js/` → JS docs
* `/api-docs/c/` → C docs

Start by locating the existing JavaScript or Rust release workflow and its GitHub Pages deployment, then inspect the automerge-c directory and the automerge_docs CMake target. Confirm where generated files should be published and how the existing JS and Rust docs are handled. Done means the C API index.html is generated during the appropriate release and linked from the website.

Written by the indexing model from the issue text.