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>

eslint.config.ts

@@ -28,14 +28,7 @@ export default tseslint.config(
 
   // 4. 核心业务全受控大管线（Hooks, Entrypoints, Components 统一护航）
   {
-    files: [
-      'hooks/**/*.{ts,tsx}',
-      'entrypoints/**/*.{ts,tsx}',
-      'pages/**/*.{ts,tsx}',
-      'utils/**/*.{ts,tsx}',
-      'components/**/*.{ts,tsx}',
-      'services/**/*.{ts,tsx}',
-    ],
+    files: ['src/**/*.{ts,tsx}'],
     ignores: ['**/__tests__/**', '**/*.test.{ts,tsx}', '**/*.spec.{ts,tsx}'],
 
     languageOptions: {