docs: use supported Amp plugin install flow

Amp-Thread-ID: https://ampcode.com/threads/T-019fd25c-ccda-74dd-bf67-2e89eca5a745
Co-authored-by: rekt <omaraziz.dev@gmail.com>

Author: ampagent

.github/README.md

@@ -45,7 +45,9 @@ The [Ponytail plugin](/plugins#ponytail) adds always-on, mode-aware
 [Ponytail](https://github.com/dietrichgebert/ponytail) support to Amp:
 
 ```bash
-amp plugins add --auto-update https://raw.githubusercontent.com/o-az/skills/main/plugins/ponytail.ts
+mkdir -p ~/.config/amp/plugins
+curl -fsSL https://raw.githubusercontent.com/o-az/skills/main/plugins/ponytail.ts \
+  -o ~/.config/amp/plugins/ponytail.ts
 ```
 
 ## Contributing a new Skill

plugins/README.md

@@ -7,14 +7,19 @@ solution that actually works. The Amp plugin applies Ponytail on every agent
 turn, keeps intensity modes isolated per thread, and exposes native controls in
 Amp's command palette.
 
-Install it as a system plugin with automatic updates:
+Install it as a system plugin on macOS or Linux:
 
 ```sh
-amp plugins add --auto-update https://raw.githubusercontent.com/o-az/skills/main/plugins/ponytail.ts
+mkdir -p ~/.config/amp/plugins
+curl -fsSL https://raw.githubusercontent.com/o-az/skills/main/plugins/ponytail.ts \
+  -o ~/.config/amp/plugins/ponytail.ts
 ```
 
 Then run `plugins: reload` from Amp's command palette or restart Amp.
 
+The current Amp CLI only accepts Amp-hosted URLs in `amp plugins add`. Rerun
+the command above to update this GitHub-hosted plugin.
+
 ### Use
 
 Ponytail starts in `full` mode. Open the command palette and use:
@@ -51,7 +56,7 @@ Set `PONYTAIL_DEFAULT_MODE=off|lite|full|ultra` to override the saved default.
 Remove the plugin with:
 
 ```sh
-amp plugins remove ponytail.ts
+rm ~/.config/amp/plugins/ponytail.ts
 ```
 
 The Ponytail instructions embedded in the plugin are adapted from

plugins/ponytail.ts

@@ -1,5 +1,3 @@
-// @amp-plugin updated automatically from https://raw.githubusercontent.com/o-az/skills/main/plugins/ponytail.ts
-
 import type { PluginAPI, PluginCommandContext, ThreadID } from "@ampcode/plugin";
 
 export const description =