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%

.gitea/workflows/release.yml

@@ -0,0 +1,31 @@
+name: Release
+on:
+  push:
+    tags:
+      - 'v*'
+
+jobs:
+  release:
+    runs-on: macos-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+      
+      - name: Setup Rust
+        uses: actions-rust-lang/setup-rust-toolchain@v1
+        with:
+          toolchain: stable
+      
+      - name: Build release
+        run: cargo build --release
+      
+      - name: Create archive
+        run: |
+          cd target/release
+          tar -czf markbase-${{ github.ref_name }}-macos-arm64.tar.gz markbase
+      
+      - name: Upload release asset
+        uses: actions/upload-artifact@v3
+        with:
+          name: markbase-${{ github.ref_name }}-macos-arm64
+          path: target/release/markbase-${{ github.ref_name }}-macos-arm64.tar.gz