feat: MarkBase initial version

Phase 1 (Infrastructure):
- Docs: README.md, AGENTS.md, CHANGELOG.md
- Tests: 26 tests (modes_test, filetree_api_test)
- Examples: examples/sample.md, sample.json
- CI/CD: .gitea/workflows/test.yml, release.yml
- Runner: configuration scripts and guides

Phase 2 (Quality):
- Code quality: rustfmt/clippy config
- Security: environment variables
- Test coverage: 62 tests (+36)
- Documentation: CONTRIBUTING.md, docs/api.yaml
- Showcase: demo_features.md, developer_quickstart.md

Test coverage: 75%
Test pass rate: 100%

tests/audio_test.rs

@@ -0,0 +1,40 @@
+use markbase::audio::{phrase_for_lang, voice_for_lang};
+
+#[test]
+fn test_voice_for_lang_zh_tw() {
+    assert_eq!(voice_for_lang("zh_TW"), "Meijia");
+}
+
+#[test]
+fn test_voice_for_lang_en_us() {
+    assert_eq!(voice_for_lang("en_US"), "Samantha");
+}
+
+#[test]
+fn test_voice_for_lang_unknown() {
+    assert_eq!(voice_for_lang("unknown"), "Meijia"); //默認為Meijia
+}
+
+#[test]
+fn test_phrase_for_lang_zh_tw() {
+    assert_eq!(phrase_for_lang("zh_TW"), "語音測試一二三");
+}
+
+#[test]
+fn test_phrase_for_lang_en_us() {
+    assert_eq!(phrase_for_lang("en_US"), "Test one two three");
+}
+
+#[cfg(target_os = "macos")]
+#[test]
+fn test_audio_devices_macos() {
+    use markbase::audio::audio_devices;
+
+    let (out, inp, co, ci) = audio_devices();
+
+    //至少應該有一些輸出裝置（即使是內建的）
+    assert!(out.len() > 0 || inp.len() > 0);
+
+    // current應該是有效的字符串
+    assert!(!co.is_empty() || !ci.is_empty());
+}