feat(FN-2493): add plugin add alias and normalize install guidance

- Route "fn plugin add" to the plugin install handler and update CLI help/usage text to document the alias
- Add bin routing tests that cover plugin add/install parity and updated error/help messaging
- Update getting-started, settings reference, and runtime plugin READMEs to standardize plugin installation examples
- Add a patch changeset for @runfusion/fusion and apply DirectoryPicker/PluginManager design-token styling refinements

docs/getting-started.md

@@ -27,7 +27,7 @@ The Paperclip Runtime Plugin (`fusion-plugin-paperclip-runtime`) provides an alt
 To install the plugin:
 
 ```bash
-fn plugin add ./plugins/fusion-plugin-paperclip-runtime
+fn plugin install ./plugins/fusion-plugin-paperclip-runtime
 ```
 
 After installation, select the Paperclip runtime for an agent by setting `runtimeHint` in the agent's `runtimeConfig`:
@@ -51,7 +51,7 @@ The Hermes Runtime Plugin (`fusion-plugin-hermes-runtime`) registers an experime
 Install the plugin:
 
 ```bash
-fn plugin add ./plugins/fusion-plugin-hermes-runtime
+fn plugin install ./plugins/fusion-plugin-hermes-runtime
 ```
 
 Configure an agent to use Hermes:
@@ -77,7 +77,7 @@ The OpenClaw Runtime Plugin (`fusion-plugin-openclaw-runtime`) registers an expe
 Install the plugin:
 
 ```bash
-fn plugin add ./plugins/fusion-plugin-openclaw-runtime
+fn plugin install ./plugins/fusion-plugin-openclaw-runtime
 ```
 
 Configure an agent to use OpenClaw:

docs/settings-reference.md

@@ -300,9 +300,9 @@ To use plugin-provided runtimes like Paperclip, Hermes, or OpenClaw:
 1. Install one or more runtime plugins:
 
 ```bash
-fn plugin add ./plugins/fusion-plugin-paperclip-runtime
-fn plugin add ./plugins/fusion-plugin-hermes-runtime
-fn plugin add ./plugins/fusion-plugin-openclaw-runtime
+fn plugin install ./plugins/fusion-plugin-paperclip-runtime
+fn plugin install ./plugins/fusion-plugin-hermes-runtime
+fn plugin install ./plugins/fusion-plugin-openclaw-runtime
 ```
 
 2. Create agents with the appropriate `runtimeConfig`: