chore: consolidate remaining tests into __tests__/ dirs and refactor mocks

Mostly mechanical cleanup left over from the earlier test-consolidation pass:
- Update import paths to ../../ for mocks now that test files moved deeper
- Simplify mock setup (drop usePluginUiSlots inline mock, etc.)
- Move engine ipc + runtimes tests into __tests__/ subdirs
- Move dashboard utils tests into __tests__/ subdir
- Refresh fusion-plugin-hermes-runtime/dist artifacts

build-exe.test.ts: spawn-import fix from a parallel branch (resolved during
worktree merge of the CSS extraction work).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

plugins/fusion-plugin-hermes-runtime/dist/pi-module.js

@@ -2,10 +2,12 @@
  * Pi Module Seam
  *
  * Provides a mockable import path for pi functions used by the HermesRuntimeAdapter.
+ * Tests intercept this module via `vi.mock("../pi-module.js", ...)`. The runtime
+ * implementations come from @fusion/engine; the local types provide a loose
+ * surface so the adapter doesn't have to depend on @fusion/engine's full types.
  */
-// eslint-disable-next-line @typescript-eslint/no-require-imports
-const _piModule = require("../../../packages/engine/src/pi.js");
-export const createFnAgent = _piModule.createFnAgent;
-export const promptWithFallback = _piModule.promptWithFallback;
-export const describeModel = _piModule.describeModel;
+import { createFnAgent as _createFnAgent, promptWithFallback as _promptWithFallback, describeModel as _describeModel, } from "@fusion/engine";
+export const createFnAgent = _createFnAgent;
+export const promptWithFallback = _promptWithFallback;
+export const describeModel = _describeModel;
 //# sourceMappingURL=pi-module.js.map