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.d.ts

@@ -1,8 +1,3 @@
-/**
- * Pi Module Seam
- *
- * Provides a mockable import path for pi functions used by the HermesRuntimeAdapter.
- */
 export interface PiAgentSession {
     dispose?: () => Promise<void> | void;
 }