docs: standardize installation instructions across all plugins

All 6 plugin READMEs now use identical installation section:
marketplace-first approach with /plugin browsing, then direct
settings.json as alternative. Replaces inconsistent mix of
git clone, plugin add, and JSON-only instructions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugins/ultraplan-local/README.md

@@ -19,8 +19,8 @@ No cloud dependency. No GitHub requirement. Works on **Mac, Linux, and Windows**
 ## Quick start
 
 ```bash
-# Install
-git clone https://git.fromaitochitta.com/open/ultraplan-local.git ~/plugins/ultraplan-local
+# Install the marketplace, then browse and enable plugins with /plugin
+claude plugin marketplace add https://git.fromaitochitta.com/open/ktg-plugin-marketplace.git
 
 # Research a question
 /ultraresearch-local Should we migrate from Express to Fastify?
@@ -362,27 +362,19 @@ If no API key is set, parallel sessions use your subscription and proceed withou
 
 ## Installation
 
-### From source
+Add the marketplace and browse plugins with `/plugin`:
 
 ```bash
-git clone https://git.fromaitochitta.com/open/ultraplan-local.git ~/plugins/ultraplan-local
+claude plugin marketplace add https://git.fromaitochitta.com/open/ktg-plugin-marketplace.git
 ```
 
-### Usage with Claude Code
-
-**One-time:**
-
-```bash
-claude --plugin-dir ~/plugins/ultraplan-local
-```
-
-**Permanent** -- add to `~/.claude/settings.json`:
+Or enable directly in `~/.claude/settings.json`:
 
 ```json
 {
-  "plugins": [
-    "~/plugins/ultraplan-local"
-  ]
+  "enabledPlugins": {
+    "ultraplan-local@ktg-plugin-marketplace": true
+  }
 }
 ```