Add Svelte support (#1457)

Uses svelte LS and typescript LS as companion server

docs/02-usage/050_configuration.md

@@ -992,6 +992,26 @@ Supported settings:
 TypeScript supports [additional workspace folders](additional-workspace-folders) for cross-package
 reference discovery. Configure `additional_workspace_folders` in `project.yml` to enable this feature.
 
+#### Svelte
+
+Serena uses `svelte-language-server` for the `svelte` language key. Use `svelte` for Svelte projects instead of also listing `typescript`, unless you intentionally want multiple language servers active for the same files.
+
+A companion TypeScript language server (`typescript-language-server` + `typescript-svelte-plugin`) is spawned automatically alongside the Svelte LSP. The plugin makes the TypeScript program `.svelte`-aware so that cross-file operations — rename, go-to-definition, and find-references from `.ts`/`.js` files — correctly include `.svelte` consumers. Serena merges and deduplicates reference results from both servers automatically.
+
+Supported settings:
+
+| Setting | Default | Description |
+|---|---|---|
+| `ls_path` | managed install | Override the `svelteserver` executable path. |
+| `svelte_language_server_version` | `0.18.0` | Override the `svelte-language-server` npm package version Serena installs. |
+| `typescript_version` | `6.0.3` (falls back to `ls_specific_settings.typescript.typescript_version`) | Override the `typescript` npm package version used as the shared tsdk. |
+| `typescript_language_server_version` | `5.1.3` (falls back to `ls_specific_settings.typescript.typescript_language_server_version`) | Override the `typescript-language-server` npm package version for the companion server. |
+| `typescript_svelte_plugin_version` | `0.3.52` | Override the `typescript-svelte-plugin` npm package version used for `.svelte`-aware TS resolution. |
+| `npm_registry` | `null` | Override the npm registry Serena uses for all managed installs. |
+| `initialization_options_configuration` | `{}` | Deep-merge overrides for any of the ten plugin configuration sections (`svelte`, `prettier`, `emmet`, `typescript`, `javascript`, `js/ts`, `css`, `less`, `scss`, `html`). |
+
+All four packages are tracked via a version file; changing any version setting triggers a clean reinstall.
+
 #### TypeScript via `vtsls`
 
 The actual configuration key for vtsls is `typescript_vts`, not `vts`.

docs/02-usage/070_security.md

@@ -150,6 +150,7 @@ Only the language servers listed below download or install additional dependenci
 - **PHP (`intelephense`)**: `intelephense`
 - **SCSS / Sass / CSS**: `some-sass-language-server`
 - **Solidity**: `@nomicfoundation/solidity-language-server`
+- **Svelte**: `svelte-language-server`
 - **TypeScript**: `typescript` and `typescript-language-server`
 - **Vue**: `@vue/language-server`, plus `typescript` and `typescript-language-server`
 - **VTSLS**: `@vtsls/language-server`