fix(FN-3794): pass unload context and isolate WhatsApp sessions per project

- Extend PluginOnUnload to receive runtime context and wire ctx through plugin-loader unload hooks
- Scope WhatsApp chat plugin connections by project root to avoid cross-project session leakage
- Update plugin authoring docs and add a patch changeset for @runfusion/fusion
- Align plugin test suites across WhatsApp and example/runtime plugins with the new onUnload context contract

Fusion-Task-Id: FN-3794

plugins/fusion-plugin-openclaw-runtime/src/__tests__/index.test.ts

@@ -144,6 +144,7 @@ describe("openclaw-runtime plugin", () => {
   });
 
   it("onUnload does not throw", () => {
-    expect(() => plugin.hooks!.onUnload?.()).not.toThrow();
+    const ctx = createMockContext() as any;
+    expect(() => plugin.hooks!.onUnload?.(ctx)).not.toThrow();
   });
 });