fix(web): link plugins to desktop app

Keep browser entry points visible while explaining that native
plugins require a desktop install.

Refs #567

docs/native-vs-web.md

@@ -81,9 +81,10 @@ on the web.
 
 Marketplace plugins are native `.dll`, `.so`, or `.dylib` packages launched in
 an isolated child process. Browsers cannot load those libraries or spawn the
-plugin runner, so the web build does not show the Plugin Manager or register
-its commands. Installed desktop plugins remain in the per-user plugins folder
-and load again on the next desktop launch.
+plugin runner. The web Plugin button and `PLUGINS` command therefore show a
+short explanation with a link to download the desktop app instead of opening
+the marketplace. Installed desktop plugins remain in the per-user plugins
+folder and load again on the next desktop launch.
 
 ### Platform shims (`src/sys.rs`)
 - `open_url`: `open::that` on native, `window.open(_blank)` on web.

docs/plugin-architecture.md

@@ -334,8 +334,9 @@ plugin dead, and reports a `CallTimeout` error via the normal plugin error path.
 ## Marketplace
 
 The desktop **Plugin Manager** (`PLUGINS` / `PLUGINMANAGER`, or the Start-page
-button) installs plugins from GitHub Releases. It is hidden in the browser
-build because marketplace packages are native dynamic libraries:
+button) installs plugins from GitHub Releases. In the browser, the same entry
+points show a desktop-download notice because marketplace packages are native
+dynamic libraries:
 
 - **Curated registry** — [`plugins/registry.json`](../plugins/registry.json) in
   this repo lists discoverable plugins. The host fetches it from `main` at