refactor: reorganize directory structure into src/

Move all source code directories into src/ for cleaner project structure:
- pages/, components/, utils/, config/, providers/, types/, lib/, assets/, entrypoints/ → src/
- Use WXT srcDir config to resolve @/ alias to src/
- Update tsconfig, vitest, eslint, tailwind configs
- Remove scattered README.md files from subdirectories
- Update documentation (AGENTS.md, CODING_STANDARDS.md, README.md)
- Fix pre-existing lint error in RouterProvider.tsx

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/utils/jwt.ts

@@ -0,0 +1,129 @@
+/**
+ * JWT 解析工具
+ */
+
+import { getMessage } from '@/utils/chromeI18n';
+
+export interface JwtHeader {
+  alg: string;
+  typ?: string;
+  [key: string]: unknown;
+}
+
+export interface JwtPayload {
+  iss?: string;
+  sub?: string;
+  aud?: string | string[];
+  exp?: number;
+  nbf?: number;
+  iat?: number;
+  jti?: string;
+  [key: string]: unknown;
+}
+
+export interface JwtResult {
+  header: JwtHeader | null;
+  payload: JwtPayload | null;
+  signature: string;
+  raw: {
+    header: string;
+    payload: string;
+    signature: string;
+  };
+  error?: string;
+}
+
+/**
+ * Base64URL 解码
+ * @param str Base64URL 编码字符串
+ */
+export function decodeBase64Url(str: string): string {
+  let base64 = str.replace(/-/g, '+').replace(/_/g, '/');
+
+  const pad = base64.length % 4;
+  if (pad) {
+    if (pad === 1) {
+      throw new Error(getMessage('jwt_errors_invalidBase64String'));
+    }
+    base64 += new Array(5 - pad).join('=');
+  }
+
+  try {
+    const binStr = atob(base64);
+    const binLen = binStr.length;
+    const bytes = new Uint8Array(binLen);
+    for (let i = 0; i < binLen; i++) {
+      bytes[i] = binStr.charCodeAt(i);
+    }
+    const decoder = new TextDecoder('utf-8');
+    return decoder.decode(bytes);
+  } catch (e) {
+    throw new Error(
+      getMessage('jwt_errors_failedToDecode') + (e instanceof Error ? e.message : String(e)),
+      { cause: e },
+    );
+  }
+}
+
+/**
+ * 解析 JWT 字符串
+ * @param token JWT 字符串
+ */
+export function parseJwt(token: string): JwtResult {
+  const parts = token.trim().split('.');
+
+  if (parts.length !== 3) {
+    return {
+      header: null,
+      payload: null,
+      signature: '',
+      raw: { header: '', payload: '', signature: '' },
+      error: getMessage('jwt_errors_invalidFormat'),
+    };
+  }
+
+  const [headerB64, payloadB64, signatureB64] = parts;
+  const result: JwtResult = {
+    header: null,
+    payload: null,
+    signature: signatureB64,
+    raw: {
+      header: headerB64,
+      payload: payloadB64,
+      signature: signatureB64,
+    },
+  };
+
+  try {
+    const headerJson = decodeBase64Url(headerB64);
+    result.header = JSON.parse(headerJson);
+  } catch (e) {
+    result.error =
+      getMessage('jwt_errors_parseHeaderFailed') + (e instanceof Error ? e.message : String(e));
+    return result;
+  }
+
+  try {
+    const payloadJson = decodeBase64Url(payloadB64);
+    result.payload = JSON.parse(payloadJson);
+  } catch (e) {
+    result.error =
+      getMessage('jwt_errors_parsePayloadFailed') + (e instanceof Error ? e.message : String(e));
+    return result;
+  }
+
+  return result;
+}
+
+/**
+ * 将对象格式化为 JSON 字符串
+ * @param obj 对象
+ */
+export function stringifyJson(obj: unknown): string {
+  try {
+    return JSON.stringify(obj, null, 2);
+  } catch (e) {
+    console.error('格式化 JSON 失败：', e);
+    return String(obj);
+  }
+}