Harden Yomitan read-only logging and extract overlay options

- Redact skipped Yomitan write log values (paths to basename, titles hidden)
- Extract overlay BrowserWindow option builder for direct unit testing
- Document and test `externalProfilePath` tilde (`~`) home expansion

src/core/services/overlay-window-options.ts

@@ -0,0 +1,39 @@
+import type { BrowserWindowConstructorOptions, Session } from 'electron';
+import * as path from 'path';
+import type { OverlayWindowKind } from './overlay-window-input';
+
+export function buildOverlayWindowOptions(
+  kind: OverlayWindowKind,
+  options: {
+    isDev: boolean;
+    yomitanSession?: Session | null;
+  },
+): BrowserWindowConstructorOptions {
+  const showNativeDebugFrame = process.platform === 'win32' && options.isDev;
+
+  return {
+    show: false,
+    width: 800,
+    height: 600,
+    x: 0,
+    y: 0,
+    transparent: true,
+    frame: false,
+    alwaysOnTop: true,
+    skipTaskbar: true,
+    resizable: false,
+    hasShadow: false,
+    focusable: true,
+    acceptFirstMouse: true,
+    ...(process.platform === 'win32' ? { thickFrame: showNativeDebugFrame } : {}),
+    webPreferences: {
+      preload: path.join(__dirname, '..', '..', 'preload.js'),
+      contextIsolation: true,
+      nodeIntegration: false,
+      sandbox: false,
+      webSecurity: true,
+      session: options.yomitanSession ?? undefined,
+      additionalArguments: [`--overlay-layer=${kind}`],
+    },
+  };
+}