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/skills/vale-config/README.md

@@ -0,0 +1,23 @@
+# vale-config
+
+Install and configure Vale, the prose/style linter — `.vale.ini`, `StylesPath`, built-in/third-party/custom styles, and activation via `BasedOnStyles`.
+
+## What it does
+
+Covers the setup side of Vale: getting a project from no config to a working `.vale.ini` where `vale sync` runs clean and every declared style is actually activated for the right files. Does not run Vale or interpret its output — see `vale-run` for that.
+
+## Usage
+
+```
+/vale-config
+```
+
+Describe what you want configured: initial setup, adding a third-party style package, or a custom rule. The skill covers install, `StylesPath` layout, `.vale.ini` structure, and `BasedOnStyles` activation.
+
+## Files
+
+| File | Purpose |
+|------|---------|
+| `SKILL.md` | Skill instructions for agents |
+| `references/configuration-reference.md` | Full `.vale.ini` field and rule-header reference |
+| `references/sources.md` | Research sources backing the Vale configuration guidance |