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/format.ts

@@ -0,0 +1,24 @@
+/**
+ * 格式化字节大小为易读字符串
+ *
+ * @param bytes 字节数
+ * @returns 格式化后的字符串，例如 "1.5 KB" 或 "100 B"
+ */
+export function formatBytes(bytes: number): string {
+  if (bytes === 0) return '0 B';
+  if (bytes < 1024) return `${bytes} B`;
+
+  const units = ['KB', 'MB', 'GB', 'TB'];
+  let size = bytes / 1024;
+  let unitIndex = 0;
+
+  while (size >= 1024 && unitIndex < units.length - 1) {
+    size /= 1024;
+    unitIndex++;
+  }
+
+  // KB uses 1 decimal, MB/GB/TB use 2 decimals
+  const decimals = unitIndex === 0 ? 1 : 2;
+
+  return `${size.toFixed(decimals)} ${units[unitIndex]}`;
+}