feat: prepare VS Code extension for marketplace

editors/vscode/PUBLISHING.md

@@ -0,0 +1,38 @@
+# Publishing the WRNexus VS Code extension
+
+The Marketplace extension identifier is `wrnexus.wrnexus`. The `wrnexus`
+publisher must exist in the Visual Studio Marketplace and the publishing
+identity must have permission to manage it.
+
+## Build and inspect the VSIX
+
+From `editors/vscode`:
+
+```powershell
+bun install
+bun run check
+bun run package
+```
+
+Install the resulting `wrnexus-<version>.vsix` in a clean VS Code profile and
+verify highlighting, Format Document, completion, snippets, and diagnostics on
+a `.wrn` file.
+
+## Publish
+
+Choose one of these supported routes:
+
+1. Upload the verified VSIX through the Visual Studio Marketplace publisher
+   management page.
+2. Authenticate `vsce` for the `wrnexus` publisher and run:
+
+   ```powershell
+   bun run publish
+   ```
+
+Never commit an Azure token or place it in a command-line argument. For local
+token-based publishing, provide it through the `VSCE_PAT` environment variable.
+For automated publishing, prefer a protected CI secret or Microsoft Entra ID.
+
+Before each release, increment `version` in `package.json`, update
+`CHANGELOG.md`, run the checks, and inspect the VSIX contents printed by `vsce`.