fix(plugins): support export default { activate }, cleanup partiel et erreurs visibles

Le loader accepte désormais aussi la forme export default { activate }
en plus de l'export nommé, les subscriptions partiellement établies
sont nettoyées en cas d'échec d'activation, et une erreur de
runtime-catalog est remontée visuellement dans PluginsPanel avec un
badge Invalide/Isolé sur les plugins concernés (#116/#120).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/plugins/runtime/loader.test.ts

@@ -52,6 +52,26 @@ describe("loadPlugins", () => {
     expect((globalThis as Record<string, unknown>).__activatedWith).toBe("dev.acme.one");
   });
 
+  it("loads an SDK-style default export containing activate(ctx)", async () => {
+    const bundle = dataUrl(`
+      export default {
+        activate(ctx) {
+          globalThis.__defaultExportActivatedWith = ctx.pluginId;
+        },
+      };
+    `);
+    const { registry, failures } = await loadPlugins(
+      [entry({ id: "com.example.hello-plugin", displayName: "Hello Plugin", bundleUrl: bundle })],
+      gateways,
+    );
+
+    expect(failures).toEqual([]);
+    expect(registry.list().map((p) => p.pluginId)).toEqual(["com.example.hello-plugin"]);
+    expect((globalThis as Record<string, unknown>).__defaultExportActivatedWith).toBe(
+      "com.example.hello-plugin",
+    );
+  });
+
   it("refuses to register a command not declared in the manifest", async () => {
     const bundle = dataUrl(`
       export function activate(ctx) {
@@ -259,6 +279,32 @@ describe("loadPlugins", () => {
     ]);
   });
 
+  it("disposes partial subscriptions when activation fails", async () => {
+    const bundle = dataUrl(`
+      export function activate(ctx) {
+        ctx.subscriptions.push({
+          dispose() {
+            globalThis.__partialActivationDisposed = ctx.pluginId;
+          },
+        });
+        throw new Error("activation failed");
+      }
+    `);
+
+    const { registry, failures } = await loadPlugins(
+      [entry({ id: "dev.acme.partial", displayName: "Partial", bundleUrl: bundle })],
+      gateways,
+    );
+
+    expect(registry.list()).toEqual([]);
+    expect(failures).toEqual([
+      { pluginId: "dev.acme.partial", reason: "activation failed" },
+    ]);
+    expect((globalThis as Record<string, unknown>).__partialActivationDisposed).toBe(
+      "dev.acme.partial",
+    );
+  });
+
   it("only loads what the catalog contains — a disabled/absent plugin is simply never in it", async () => {
     // The backend contract (carnet §1.3) filters the catalog to
     // `enabled && !pendingUninstall` before the loader ever sees it; the