Add cross-reference map, admin health page, passkeys and device list, settings tabs

- Reader: chapter cross-reference map (M) from IQ Bible's reference graph
- Admin: Health tab with disk use, snapshots (back up, download, restore), failure logs
- Passkey sign-in (WebAuthn), signed-in device list, sign out others, optional sign-in alerts
- Settings split into Account, Preferences, Notifications, Security, Your data tabs
- ntfy server field: catch a topic typed into the server box

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

package.json

@@ -18,6 +18,8 @@
     "lint": "eslint ."
   },
   "dependencies": {
+    "@simplewebauthn/browser": "^13.3.0",
+    "@simplewebauthn/server": "^13.3.3",
     "bcryptjs": "^3.0.3",
     "better-sqlite3": "^12.10.0",
     "compression": "^1.8.2",