refactor(main): add runtime domain registry and fan-in guardrails

Introduce runtime domain barrel exports and registry composition support, and document/check main runtime fan-in workflow with related backlog planning artifacts.

src/main/runtime/registry.test.ts

@@ -0,0 +1,46 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+
+async function loadRegistryOrSkip(t: test.TestContext) {
+  try {
+    return await import('./registry');
+  } catch (error) {
+    if (error instanceof Error && error.message.includes('node:sqlite')) {
+      t.skip('registry import requires node:sqlite support in this runtime');
+      return null;
+    }
+    throw error;
+  }
+}
+
+test('createMainRuntimeRegistry exposes expected runtime domains', async (t) => {
+  const loaded = await loadRegistryOrSkip(t);
+  if (!loaded) return;
+  const { createMainRuntimeRegistry } = loaded;
+  const registry = createMainRuntimeRegistry();
+
+  assert.ok(registry.anilist);
+  assert.ok(registry.jellyfin);
+  assert.ok(registry.overlay);
+  assert.ok(registry.startup);
+  assert.ok(registry.mpv);
+  assert.ok(registry.shortcuts);
+  assert.ok(registry.ipc);
+  assert.ok(registry.mining);
+});
+
+test('registry domains expose representative factories', async (t) => {
+  const loaded = await loadRegistryOrSkip(t);
+  if (!loaded) return;
+  const { createMainRuntimeRegistry } = loaded;
+  const registry = createMainRuntimeRegistry();
+
+  assert.equal(typeof registry.anilist.createNotifyAnilistSetupHandler, 'function');
+  assert.equal(typeof registry.jellyfin.createRunJellyfinCommandHandler, 'function');
+  assert.equal(typeof registry.overlay.createOverlayVisibilityRuntime, 'function');
+  assert.equal(typeof registry.startup.createStartupRuntimeHandlers, 'function');
+  assert.equal(typeof registry.mpv.createMpvClientRuntimeServiceFactory, 'function');
+  assert.equal(typeof registry.shortcuts.createGlobalShortcutsRuntimeHandlers, 'function');
+  assert.equal(typeof registry.ipc.createIpcRuntimeHandlers, 'function');
+  assert.equal(typeof registry.mining.createMineSentenceCardHandler, 'function');
+});