feat(lint): add vale-config skill

Covers Vale install and .vale.ini setup — StylesPath, built-in/
third-party/custom styles, BasedOnStyles activation. Setup half of
Vale support; vale-run (running/interpreting) is a separate skill.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FxG5T8EJDgkABXxuneuFfn

plugins/lint/docs/research/docs/vale/installation.md

@@ -0,0 +1,41 @@
+---
+topic: installation
+source_keys:
+  - context7-websites-vale-sh
+---
+
+## Package Managers
+
+Vale is distributed via standard OS package managers:
+
+```bash
+brew install vale      # macOS
+snap install vale      # Linux
+```
+
+```powershell
+choco install vale      # Windows
+```
+
+## Docker
+
+An official image is available on Docker Hub:
+
+```bash
+docker pull jdkato/vale
+```
+
+## Post-Install: Syncing Styles
+
+Installing the `vale` binary alone does not install any styles. After install, run `vale sync` to download and install the styles/packages declared in `.vale.ini`:
+
+```bash
+$ vale sync
+```
+
+## Format-Specific Extras
+
+Some input formats need an external converter installed separately before Vale can process them:
+
+- reStructuredText: `pip install docutils` (provides `rst2html`)
+- MDX: `npm install -g mdx2vast`