🚀 feat(frontend): add robust boolean handling across settings pages

Summary
-------
1. Introduced a reusable `toBoolean` utility (`web/src/helpers/boolean.js`) that converts
   strings (`'true'/'false'`, `'1'/'0'`), numbers, and native booleans to a proper boolean.
2. Re-exported `toBoolean` via `web/src/helpers/index.js` for simple one-line imports.

Refactors
---------
• Systematically replaced all legacy `item.value === 'true'` checks with `toBoolean(item.value)` in
  the following components:
  – `SystemSetting.js`
  – `OperationSetting.js`
  – `PaymentSetting.js`
  – `RatioSetting.js`
  – `RateLimitSetting.js`
  – `ModelSetting.js`
  – `DrawingSetting.js`
  – `DashboardSetting.js`
  – `ChatsSetting.js`

• Unified import statements to
  `import { …, toBoolean } from '../../helpers';`
  removing redundant `../../helpers/boolean` paths.

Why
---
SQLite sometimes returns `1/0` or boolean literals instead of the string `'true'/'false'`, causing
checkbox states to reset on page reload. The new utility guarantees consistent boolean parsing,
fixing the issue across all environments (SQLite, MySQL, etc.) while improving code clarity.

web/src/helpers/boolean.js

@@ -0,0 +1,10 @@
+export const toBoolean = (value) => {
+  // 兼容字符串、数字以及布尔原生类型
+  if (typeof value === 'boolean') return value;
+  if (typeof value === 'number') return value === 1;
+  if (typeof value === 'string') {
+    const v = value.toLowerCase();
+    return v === 'true' || v === '1';
+  }
+  return false;
+};