fix: address CodeRabbit review findings across runtime modules

- Extract filterLegacyMpvPluginFileCandidates, buildYomitanAnkiSettingsKey, setMpvCurrentSecondarySubText, runSupportAssetUpdatesForLauncherResult helpers
- Include forceOverride in yomitan anki settings cache key (was missing, causing incorrect cache hits)
- Detect same-PID stale stats daemon state to avoid self-connect
- Validate non-empty extension in buildFfmpegSubtitleExtractionArgs
- Drop unused message param from showOverlayLoadingStatusNotification
- Log and rethrow on session bindings artifact write failure
- Add unit tests for all extracted helpers

src/main/runtime/update/update-service-runtime.test.ts

@@ -0,0 +1,20 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { runSupportAssetUpdatesForLauncherResult } from './update-support-assets-runtime';
+
+test('runSupportAssetUpdatesForLauncherResult logs support-asset errors and preserves launcher result', async () => {
+  const warnings: string[] = [];
+  const launcherResult = { status: 'updated' } as const;
+  const result = await runSupportAssetUpdatesForLauncherResult({
+    launcherResult,
+    updateSupportAssets: async () => {
+      throw new Error('archive failed');
+    },
+    logWarn: (message, details) => {
+      warnings.push(`${message}:${details instanceof Error ? details.message : String(details)}`);
+    },
+  });
+
+  assert.equal(result, launcherResult);
+  assert.deepEqual(warnings, ['Support asset update failed after launcher update:archive failed']);
+});