feat: add Zed extension release artifact with WSL2 support

The Zed extension now detects Windows via current_platform() and
automatically uses `wsl streamd lsp` instead of `streamd lsp`,
enabling seamless LSP support when Zed runs on Windows with streamd
installed in WSL2.

A pre-built zip (extension.toml + extension.wasm) is now built as
`zed-extension-zip` and published to every release. The README gains
a step-by-step WSL2 installation guide.

README.md

@@ -153,6 +153,41 @@ Add to `~/.config/zed/settings.json`:
 
 The `"..."` keeps Zed's default Markdown servers (e.g. `marksman`) active alongside streamd.
 
+#### Zed Extension (WSL2)
+
+If you run Zed on Windows with streamd installed inside WSL2, use the pre-built Zed extension instead of the manual config above. The extension auto-detects Windows and routes LSP communication through WSL2.
+
+**1. Install streamd in WSL2** (e.g. via the `.deb` package):
+
+```bash
+wget https://git.konstantinfickel.de/kfickel/streamd/releases/download/vX.Y.Z/streamd_X.Y.Z_amd64.deb
+sudo dpkg -i streamd_X.Y.Z_amd64.deb
+```
+
+**2. Download the extension** from the same release page:
+
+```
+streamd-zed-extension-X.Y.Z.zip
+```
+
+**3. Extract the zip** to a permanent folder on your Windows machine, e.g.:
+
+```
+C:\Users\<you>\zed-extensions\streamd-zed-extension\
+```
+
+The folder must contain `extension.toml` and `extension.wasm`.
+
+**4. Install the extension in Zed** via the command palette (`Ctrl+Shift+P`):
+
+```
+zed: install dev extension
+```
+
+Point Zed to the extracted folder.
+
+**5. Verify** by opening a Markdown file inside a directory that contains `.streamd.toml` — `@` completions and diagnostics should become active.
+
 ### Neovim (nvim-lspconfig)
 
 **1. Register the server** — add to your Neovim config (e.g. `~/.config/nvim/init.lua` or a plugin file):