CONTRIBUTING.md contains unreplaced project name placeholders

**Describe the bug**

`CONTRIBUTING.md` still contains four unreplaced `{project_name}` placeholders. Two of them are used in the Issues and Pull Requests URLs, so those links currently return HTTP 404. The other two make the fork and pull-request destination instructions ambiguous.

**To Reproduce**

1. Open `CONTRIBUTING.md` on the default branch.
2. Follow the "Github Issues" link under "How to Find Known Issues" or the "GitHub" link under "Submit a Pull Request".
3. Observe that the URL points to `coze-dev/{project_name}` and returns 404.
4. Search the file for `{project_name}` and observe four remaining occurrences.

**Expected behavior**

The contribution guide should name `coze-dev/coze-studio` (and the `coze-studio:main` PR target) directly so its links and instructions are actionable.

**Screenshots**

Not applicable; the two affected URLs return HTTP 404.

**Version:**

Default branch `main`, commit `fefb05ff27be1da939612fbf9faf5db62583b8ae`.

**Environment:**

Not applicable; this is a documentation issue reproducible in a browser.

**Additional context**

I searched open and closed issues and pull requests for the literal URL, placeholder wording, and broken `CONTRIBUTING.md` links, and found no existing report or patch.

Start with CONTRIBUTING.md on the default branch and search for all four `{project_name}` occurrences. Check the Issues and Pull Requests links and the fork and PR destination instructions against the expected `coze-dev/coze-studio` repository and `coze-studio:main` target. Done means the four placeholders are gone and the links no longer point to 404 URLs.

Written by the indexing model from the issue text.