chore: 初始化工程骨架、许可与开发规范

建立仓库目录结构、许可证与贡献约定，确认前后端技术选型。

CONTRIBUTING.md

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+# Contributing to ChatterMate
+
+Thanks for your interest in contributing! This document explains how to get
+your changes accepted.
+
+## License
+
+The ChatterMate open-source core is licensed under the
+[Apache License 2.0](LICENSE). By contributing, you agree that your
+contributions will be licensed under Apache-2.0.
+
+## Developer Certificate of Origin (DCO)
+
+We use the [Developer Certificate of Origin](DCO) (DCO 1.1) instead of a CLA.
+It is a lightweight way for you to certify that you wrote, or otherwise have
+the right to submit, the code you are contributing.
+
+**Every commit must be signed off.** Add a `Signed-off-by` trailer to each
+commit message with:
+
+```bash
+git commit -s -m "your message"
+```
+
+This appends a line like:
+
+```
+Signed-off-by: Your Name <your.email@example.com>
+```
+
+The name and email must match your `git config user.name` and
+`user.email`, and must be your real identity (no anonymous or pseudonymous
+contributions).
+
+The [DCO app](https://github.com/apps/dco) runs on every pull request and
+verifies that all commits are signed off. PRs with unsigned commits will fail
+the check.
+
+### Fixing commits that are not signed off
+
+- **Last commit:** `git commit --amend -s --no-edit`
+- **A whole branch:** `git rebase --signoff main`
+
+Then force-push your branch (`git push --force-with-lease`).
+
+### Tip: never forget `-s`
+
+You can make sign-off the default for this repo with a git hook:
+
+```bash
+cat > .git/hooks/prepare-commit-msg <<'EOF'
+#!/bin/sh
+NAME=$(git config user.name)
+EMAIL=$(git config user.email)
+grep -qs "^Signed-off-by:" "$1" || printf "\nSigned-off-by: %s <%s>\n" "$NAME" "$EMAIL" >> "$1"
+EOF
+chmod +x .git/hooks/prepare-commit-msg
+```
+
+## Development workflow
+
+1. Fork the repository and create a feature branch:
+   `git checkout -b feature/amazing-feature`
+2. Make your changes. Follow the existing code style
+   (PEP 8 for Python, type hints where practical; the project conventions for
+   Vue/TypeScript on the frontend).
+3. Add or update tests for your change and make sure the suite passes. If it
+   changes something a user does, add or update the end-to-end spec too (see
+   [e2e/AUTHORING.md](e2e/AUTHORING.md)).
+4. Commit with sign-off (`git commit -s`).
+5. Push and open a Pull Request, filling out the PR template.
+
+## License headers
+
+New source files should carry the standard Apache-2.0 header. You can apply or
+refresh headers across the codebase by running:
+
+```bash
+python relicense_headers.py
+```
+
+This is idempotent — it only changes files whose header is missing or outdated.
+
+## Enterprise features
+
+Advanced/enterprise capabilities live in separate, proprietary modules and are
+**not** covered by the Apache-2.0 license. Contributions in this repository
+apply to the open-source core only.