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%

.clippy.toml

@@ -0,0 +1,13 @@
+# Clippy lint配置
+
+#允許的最低Rust版本
+msrv = "1.92"
+
+# cognitive-complexity限制
+cognitive-complexity-threshold = 25
+
+#類型複雜度限制
+type-complexity-threshold = 250
+
+# too-many-arguments限制
+too-many-arguments-threshold = 7