docs: add CI process documentation and update CONTRIBUTING structureHEADmain

Add ABOUT-CI.md describing the local CI workflow, execution stages,
and workspace cleanliness checks. Reformat CONTRIBUTING.md tables
and add a reference to the new CI documentation.

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+# About Mingling CI Process
+
+Mingling's CI process is built into the project, with its execution logic located in `dev_tools/src/bin/ci.rs`. You can run it locally via the `cargo ci` command, which produces the same results as the `CI` workflow in GitHub Actions.
+
+During development, you can run `cargo ci` at any time to verify that your code hasn't introduced regressions.
+
+## Running Locally
+
+An alias is defined in `.cargo/config.toml` at the project root:
+
+```toml
+[alias]
+ci = "run --manifest-path dev_tools/Cargo.toml --bin ci --quiet --"
+```
+
+Simply execute:
+
+```bash
+cargo ci
+```
+
+## CI Execution Flow
+
+`cargo ci` runs the following stages in order:
+
+### 1. Code Checking Stage (run by default, or individually via `--test-codes`)
+
+- **Scan and build all crates**: Recursively finds all `Cargo.toml` files in the project and runs `cargo build` for each crate in parallel.
+- **Run Clippy on all crates**: Executes `cargo clippy ... -- -D warnings` in parallel; any warning will cause a failure.
+- **Run unit tests for all crates**: Executes `cargo test` in parallel.
+
+### 2. Documentation and Example Checking Stage (run by default, or individually via `--test-docs`)
+
+- **Test all examples**: Runs the `test-examples` tool.
+- **Verify Markdown code blocks compile**: Runs the `test-all-markdown-code` tool to check code blocks in all `*.md` files. See [ABOUT_CODE_VERIFY](docs/_ABOUT_CODE_VERIFY.md) for details.
+- **Check if documentation is up to date**: Runs the following documentation refresh tools in sequence:
+    - `docs-code-box-fix`
+    - `docsify-sidebar-gen`
+    - `refresh-docs`
+    - `refresh-feature-mod`
+    - `sync-examples`
+- Finally, runs `cargo fmt` to unify code formatting.
+
+### 3. File Normalization
+
+Runs `git add --renormalize .` to ensure file attributes such as line endings conform to the repository configuration.
+
+## Workspace Cleanliness and Temporary Commits
+
+To ensure reproducible CI results, `ci.rs` imposes strict requirements on the workspace state:
+
+- If the current workspace is not clean and `--dirty` has not been specified, the script will prompt whether to create a temporary commit:
+    - The commit message is `[DO NOT PUSH] CI TEMP [DO NOT PUSH]`.
+    - Use `-y` to auto-confirm without interaction.
+- After CI finishes, the script automatically restores the workspace:
+    - First, `git reset --hard` discards all changes.
+    - If a temporary commit was created, it then runs `git reset --soft HEAD~1` and unstages everything, restoring the state to before CI started.
+- If `--dirty` is specified, the temporary commit and the final cleanliness check are skipped.
+
+> **Warning**: `git reset --hard` is executed at the end of CI. If you use `--dirty`, ensure you have no unsaved important changes.
+
+## GitHub Actions Workflow
+
+`.github/workflows/ci.yml` defines the project's CI:
+
+- Triggered on `push` to the `main` branch.
+- Runs `cargo ci` in parallel on `ubuntu-latest` and `windows-latest`.
+- After CI passes, the `unreleased` tag is automatically moved to the latest commit on `main`.