feat(plugin): add a Plugin Manager window listing installed add-ons

Read-only inventory of the add-ons compiled into the build — name, version,
id, API level, description, command prefixes — built from the extracted
`ocs_plugin_api` manifest. Opened with the `PLUGINS` / `PLUGINMANAGER` command
or the Start-page "Plugins" button.

Adds `installed_manifests()` to the plugin registry and wires the window the
same way as the existing About / Shortcuts windows.

Part of #100 (phase-1 plugin manager UI stub).

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/plugin/mod.rs

@@ -10,4 +10,4 @@ pub mod registry;
 
 pub use registry::all_ribbon_modules;
 pub(crate) use host::BuiltinPlugin;
-pub(crate) use registry::try_dispatch;
+pub(crate) use registry::{installed_manifests, try_dispatch};

src/plugin/registry.rs

@@ -1,6 +1,7 @@
 // Compile-time plugin registry via `inventory`.
 
 use super::host::{BuiltinPlugin, HostSession};
+use super::manifest::PluginManifest;
 use crate::app::OpenCADStudio;
 use crate::modules::{registry as core_registry, CadModule};
 
@@ -18,6 +19,15 @@ pub fn all_plugins() -> Vec<Box<dyn BuiltinPlugin>> {
         .collect()
 }
 
+/// Static manifest of every installed add-on, sorted by `ribbon_order` then id
+/// for a stable display. Used by the plugin manager window.
+pub fn installed_manifests() -> Vec<&'static PluginManifest> {
+    let mut manifests: Vec<&'static PluginManifest> =
+        all_plugins().iter().map(|p| p.manifest()).collect();
+    manifests.sort_by(|a, b| a.ribbon_order.cmp(&b.ribbon_order).then(a.id.cmp(b.id)));
+    manifests
+}
+
 /// Core ribbon tabs plus add-on tabs (sorted by `manifest.ribbon_order`).
 pub fn all_ribbon_modules() -> Vec<Box<dyn CadModule>> {
     let mut core = core_registry::all_modules();
@@ -61,6 +71,25 @@ mod tests {
         );
     }
 
+    #[test]
+    fn installed_manifests_lists_demo_plugin() {
+        let manifests = installed_manifests();
+        assert!(
+            manifests.iter().any(|m| m.id == "opencad.demo_plugin"),
+            "ids: {:?}",
+            manifests.iter().map(|m| m.id).collect::<Vec<_>>()
+        );
+        // Sorted by (ribbon_order, id) — verify non-decreasing order.
+        let mut prev: Option<(i32, &str)> = None;
+        for m in &manifests {
+            let key = (m.ribbon_order, m.id);
+            if let Some(p) = prev {
+                assert!(p <= key, "manifests not sorted: {p:?} then {key:?}");
+            }
+            prev = Some(key);
+        }
+    }
+
     #[test]
     fn addon_ribbon_tabs_merge_after_core() {
         let titles: Vec<&str> = all_ribbon_modules().iter().map(|m| m.title()).collect();