docs: add Documenter.jl documentation system (#288)

Set up comprehensive documentation using Documenter.jl with the following
structure:
- Getting started guide (VSCode and other editors)
- User guide (configuration, formatting, TestRunner integration)
- Communication channels documentation

Key changes:
- Create `docs/` directory with structured markdown documentation
- Add `docs/make.jl` for building documentation with Documenter.jl
- Set up GitHub Actions workflow for automated documentation deployment
- Move screenshot assets from `assets/` to `docs/src/assets/`
- Implement theme-aware image switching (light/dark mode) using custom CSS
- Add support for Catppuccin themes (Frappé, Macchiato, Mocha)
- Update README.md to focus on development information and link to docs
- Add documentation badge to README.md
- Update .gitignore to exclude docs/build/ directory

The documentation is now available at https://aviatesk.github.io/JETLS.jl/dev/
and provides a better user experience with proper navigation, search
functionality, and theme support.

Author: aviatesk

.github/workflows/docs.yml

@@ -0,0 +1,37 @@
+name: Documentation
+
+on:
+  push:
+    branches:
+      - master # update to match your development branch (master, main, dev, trunk, ...)
+    tags: '*'
+  pull_request:
+
+jobs:
+  build:
+    # These permissions are needed to:
+    # - Deploy the documentation: https://documenter.juliadocs.org/stable/man/hosting/#Permissions
+    # - Delete old caches: https://github.com/julia-actions/cache#usage
+    permissions:
+      actions: write
+      contents: write
+      pull-requests: read
+      statuses: write
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: julia-actions/setup-julia@v2
+        with:
+          version: '1'
+      - uses: julia-actions/cache@v2
+      - name: Install dependencies
+        shell: julia --color=yes --project=docs {0}
+        run: |
+          using Pkg
+          Pkg.develop(PackageSpec(path=pwd()))
+          Pkg.instantiate()
+      - name: Build and deploy
+        run: julia --color=yes --project=docs docs/make.jl
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} # If authenticating with GitHub Actions token
+          DOCUMENTER_KEY: ${{ secrets.DOCUMENTER_KEY }} # If authenticating with SSH deploy key

.gitignore

@@ -5,3 +5,4 @@ Manifest-*.toml
 .envrc
 **/.JETLSConfig.toml
 *.vsix
+docs/build/