docs: 开源规范化 — doc comments + 社区文件 + 示例代码 + crates.io 就绪

- 为 core 公开 API 添加完整 doc comments（rustdoc 可用）
- 新增 .editorconfig / CONTRIBUTING / CODE_OF_CONDUCT / SECURITY
- 新增 Issue 模板（bug + feature）+ PR 模板
- 新增 3 个代码示例（examples/）
- 更新 Cargo.toml 元数据（description/repository/keywords/categories/MSRV）
- 更新 README + CHANGELOG

core/Cargo.toml

@@ -4,9 +4,29 @@ version.workspace = true
 edition.workspace = true
 license.workspace = true
 authors.workspace = true
+description.workspace = true
+repository.workspace = true
+homepage.workspace = true
+documentation.workspace = true
+readme.workspace = true
+keywords.workspace = true
+categories.workspace = true
+rust-version.workspace = true
 
 [dependencies]
 image = { version = "0.25", default-features = false, features = ["png"] }
 serde = { version = "1", features = ["derive"] }
 
 [dev-dependencies]
+
+[[example]]
+name = "basic_qr"
+path = "../examples/basic_qr.rs"
+
+[[example]]
+name = "high_ecc"
+path = "../examples/high_ecc.rs"
+
+[[example]]
+name = "custom_config"
+path = "../examples/custom_config.rs"