feat(FN-3396): bundle Cursor CLI as a plugin provider with dashboard auth w

Merges FN-3396's full Cursor CLI provider integration (Steps 1–4): defines a CLI-backed provider contract, adds the `fusion-plugin-cursor-runtime` plugin package with process management and runtime probes, wires dashboard auth flows and UI (ProviderCard, onboarding modal, settings), and bundles the

Fusion-Task-Id: FN-3396

plugins/fusion-plugin-cursor-runtime/src/runtime-adapter.ts

@@ -0,0 +1,25 @@
+export class CursorRuntimeAdapter {
+  readonly id = "cursor";
+  readonly name = "Cursor Runtime";
+
+  async createSession(options: { defaultModelId?: string; systemPrompt?: string }) {
+    return {
+      session: {
+        model: options.defaultModelId ?? "cursor/default",
+        systemPrompt: options.systemPrompt,
+        messages: [],
+      },
+      sessionFile: undefined,
+    };
+  }
+
+  async promptWithFallback(): Promise<void> {
+    // TODO(FN-3396): Implement Cursor agent prompt streaming once a stable
+    // invocation contract beyond probe/discovery commands is confirmed.
+    return;
+  }
+
+  describeModel(session: { model?: string }) {
+    return `cursor/${session.model ?? "default"}`;
+  }
+}