add a centralized STYLE_GUIDE in Karmada for consistent AI-assisted code reviews

[zhzhuang-zju]

What type of PR is this?
/kind documentation

What this PR does / why we need it:
Currently, Gemini maintains its own style guide. To simplify maintenance and ensure consistency across tools, I propose adding a single STYLE_GUIDE.md file directly in the Karmada repository. All agents (Gemini, Copilot, etc.) can then reference this shared guide—keeping their context aligned while still allowing tool-specific customization.

Test Reports:
JesseStutler#2 (comment) (copilot)
zhzhuang-zju#14 (comment) (Gemini)

Which issue(s) this PR fixes:

Parts of #7055

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[karmada-bot]

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[gemini-code-assist]

Summary of Changes

Hello @zhzhuang-zju, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request centralizes the code style and quality guidelines for the Karmada project by introducing a new CODE_STYLE_GUIDE.md file. This initiative aims to ensure consistency across the codebase, particularly for AI-assisted tools like Copilot and Gemini, which will now reference this unified guide. The comprehensive guidelines cover various aspects of Go development, secure coding, and release note formatting, intending to simplify maintenance, reduce review iterations, and improve overall code quality.

Highlights

• Centralized Style Guide: Introduced a new CODE_STYLE_GUIDE.md file to establish a single, consistent set of coding standards for the Karmada project.
• AI Tool Integration: Updated .github/copilot-instructions.md to direct AI-assisted tools like Copilot to reference the new centralized style guide, promoting uniformity in code reviews and generated content.
• Comprehensive Guidelines: The new style guide provides detailed rules for Go code comments, compile-time interface compliance checks, function parameter best practices, secure coding specifications, and standardized CHANGELOG entry formatting.

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Ignored Files

• Ignored by pattern: .gemini/** (1)
  • .gemini/styleguide.md

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[gemini-code-assist]

Code Review

This pull request introduces a centralized style guide for AI-assisted code reviews, which is a great initiative for ensuring consistency across the project. The new documentation is well-structured. I have provided a few minor suggestions to improve clarity and maintainability, such as updating a hardcoded link to prevent it from becoming stale and fixing some small typos. I also noted a minor inconsistency in the naming of the style guide file compared to the PR description and suggested a change for better alignment. Overall, these changes are beneficial and will help streamline the review process.

[gemini-code-assist]

The link to the golangci-lint configuration uses a specific commit hash. This can become outdated as the CI workflow evolves. It's better to use a branch name like master to ensure the link always points to the latest version of the file.

Suggested change

	enforced via [golangci-lint](https://github.com/karmada-io/karmada/blob/e2c4b596a5da442fc0dbeab9f9063d8db8669208/.github/workflows/ci.yml#L18-L35).
	enforced via [golangci-lint](https://github.com/karmada-io/karmada/blob/master/.github/workflows/ci.yml#L18-L35).

[RainbowMango]

+1
It seems sensible.

[gemini-code-assist]

For better readability and to follow standard sentence capitalization, 'using' should be capitalized.

Suggested change

	using the following pattern:
	Using the following pattern:

[RainbowMango]

+1

[gemini-code-assist]

There's a small typo in the heading. It should be CHANGELOG (Release Notes) with a space for better readability.

Suggested change

	## CHANGELOG(Release Notes)
	## CHANGELOG (Release Notes)

[RainbowMango]

+1

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 46.56%. Comparing base (ffa0dfb) to head (fda9f9c).
⚠️ Report is 17 commits behind head on master.
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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7073   +/-   ##
=======================================
  Coverage   46.55%   46.56%           
=======================================
  Files         700      700           
  Lines       48084    48084           
=======================================
+ Hits        22387    22390    +3     
+ Misses      24013    24011    -2     
+ Partials     1684     1683    -1     

Flag	Coverage Δ
unittests	46.56% <ø> (+<0.01%)	⬆️

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[RainbowMango]

/assign

[RainbowMango]

One more thing, I don't want to put too many configuration files under the repo root directory.
Is it possible to put the code style file under .github directory and let Gemini read the file from there?

[zhzhuang-zju]

One more thing, I don't want to put too many configuration files under the repo root directory. Is it possible to put the code style file under .github directory and let Gemini read the file from there?

Theoretically, it's possible. I will give it a try.