chore: add contributing guide

Author: wooway777

CONTRIBUTING.md

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+# Contributing Guide
+
+For development setup, see [Development Guide](#development-guide) below.
+
+## Code
+
+Please review these details before committing, especially for AI-generated code.
+
+### General
+
+1. Keep changes minimal — do not add what is not necessary.
+2. Comments are not always better when abundant. Ideally, the code should be self-explanatory.
+3. Files must end with a newline.
+4. Use Markdown syntax (backtick-fenced) for identifiers in comments and error messages.
+5. Comments and error messages must be in English.
+6. Comments and error messages should follow the language's conventions first. If the language does not specify, use complete sentences — capitalize the first letter and end with punctuation.
+
+### C++
+
+1. Unless specified in [Adapt New Models](MODELS.md), follow the [Google C++ Style Guide](https://google.github.io/styleguide/cppguide.html) strictly. Use the default `.clang-format`.
+2. Error and warning messages follow the [LLVM Coding Standards](https://llvm.org/docs/CodingStandards.html#error-and-warning-messages).
+3. Initializer list order must match member declaration order.
+4. Formatted by `scripts/format.py`
+
+### Python
+
+Unless specified in [Adapt New Models](MODELS.md), follow [PEP 8](https://peps.python.org/pep-0008/) as the primary style guide. For anything PEP 8 does not cover in detail, refer to the [GDScript style guide](https://docs.godotengine.org/en/stable/tutorials/scripting/gdscript/gdscript_styleguide.html)—while it targets a different language, its non-syntax conventions are still applicable.
+
+Formatted by `scripts/format.py`
+
+#### Additional Rules
+
+1. **Comments** should be complete English sentences, starting with a capital letter and ending with punctuation. Use Markdown syntax when referencing code within comments.
+
+2. **Docstrings:** Follow [PEP 257](https://peps.python.org/pep-0257/) conventions.
+
+3. Formatted by `scripts/format.py`
+
+## Commits
+
+Commit messages must follow [Conventional Commits](https://www.conventionalcommits.org/).
+
+Existing commit messages may follow the "issue/### - " legacy format with an issue created to describe the case.
+
+## Pull Requests
+
+1. Small PRs should be squashed. Large PRs may keep multiple commits, but each commit must be meaningful and well-formed.
+2. PR titles should respect to issue number and case summary.
+3. Before merging (or after each stage of changes), build and test on major involved platforms. Include the results in PRs.
+
+## Branches
+
+Branch names use the format `<type>/xxx-yyyy-zzzz`, where `<type>` matches the PR title's Conventional Commits type, and words are joined with hyphens.
+
+Existing branch names may use the legacy format `issue/###`, followed by a suffix when necessary.
+
+---
+
+# Development Guide
+
+Refer to [ReadMe](README.md) and [Adapt New Models](MODELS.md)
+
+## Troubleshooting
+
+1. to be populated