fix(web): hide unsupported plugin manager

Fixes #567

docs/native-vs-web.md

@@ -18,6 +18,7 @@ browser can't provide. This page lists the differences.
 | Parallelism | Multi-threaded (rayon) | Single-threaded |
 | GPU backend | Vulkan / DX12 / Metal (wgpu) | WebGL2 (WebGPU where available) |
 | Update check / external links | `ureq`, `open` | skipped / `window.open` |
+| External plugins | Native packages + Plugin Manager | **No** — native libraries cannot run in a browser |
 
 ## Details
 
@@ -76,6 +77,14 @@ native and sequential `std` iterators on wasm, so the same call sites run in
 parallel on the desktop and serially in the browser. Large drawings are slower
 on the web.
 
+### External plugins — web: unavailable
+
+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.
+
 ### Platform shims (`src/sys.rs`)
 - `open_url`: `open::that` on native, `window.open(_blank)` on web.
 - `download_bytes`: web only (Blob + anchor download).

docs/plugin-architecture.md

@@ -333,8 +333,9 @@ plugin dead, and reports a `CallTimeout` error via the normal plugin error path.
 
 ## Marketplace
 
-The **Plugin Manager** (`PLUGINS` / `PLUGINMANAGER`, or the Start-page button)
-installs plugins from GitHub Releases:
+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:
 
 - **Curated registry** — [`plugins/registry.json`](../plugins/registry.json) in
   this repo lists discoverable plugins. The host fetches it from `main` at
@@ -343,7 +344,7 @@ installs plugins from GitHub Releases:
   [`plugins/README.md`](../plugins/README.md)); merged PRs reach every user with
   no app update.
 - **Manual link** — *Add a repository* (`owner/repo`) for unlisted or private
-  dev repos; linked repos persist in `settings.txt` (`plugin_repos=`).
+  dev repos; linked repos persist in `settings.json`.
 - **Install / upgrade / reinstall** — pick a release from the dropdown and
   *Install*; the host downloads the platform asset + `plugin.toml` into the
   plugins folder, checking `api_version` first. Reinstalling overwrites and