[Docs] Document Ditto config provider plugin

docs/plugins/ditto.md

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+# Ditto Plugin
+
+## Overview
+
+The Ditto plugin manages configuration of Ditto via config.yaml.
+
+## Prerequisites
+
+- Ditto installed
+
+## Configuration Schema
+
+Ditto's settings aren't a fixed list — you can put any key you want under settings:, and it gets copied as-is into Ditto's settings file. To find real setting names, open Ditto's own Options window on your computer (General tab, Keyboard Shortcuts tab, etc.) and see what's there.
+
+
+
+## Usage Examples
+
+### ditto config
+
+```yaml
+extensions:
+  ditto:
+    settings:
+      MaxItemsInList: 100
+    dryRun: true
+```
+
+## Verification Steps
+
+```bash
+type "%APPDATA%\Ditto\Ditto.settings"
+```
+
+## Notes / Caveats
+- Although the file is named `Ditto.settings`, its contents are JSON, not plain text.
+- Merges are shallow and non-validating: only top-level keys you specify are added or overwritten, and the plugin does not check that a key is a real Ditto setting before writing it.
+- Use `dryRun: true` to preview a change without writing to disk.