docs: use Prettier for rs fmt

[chenjiahan]

Rstack CLI plans to use Prettier to implement rs fmt, while the README still attributes formatting to Oxfmt.

This PR updates the README overview and command table to reference Prettier.

[coderabbitai]

📝 Walkthrough

Walkthrough

Updated the README to replace Oxfmt references with Prettier in the Rstack CLI overview and the rs fmt command table, including the formatter attribution link.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is concise and accurately summarizes the main change: switching rs fmt documentation to Prettier.
Description check	✅ Passed	The description directly matches the README update and references the same Prettier vs. Oxfmt change.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chenjiahan/docs-prettier-fmt

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@README.md`:
- Line 13: Update README.md lines 13-13 and 24-24 to reference Oxfmt
consistently with the current formatter configuration and rs fmt implementation;
do not document Prettier unless the formatter implementation and dependencies
are migrated first.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 5bac862b-a9d8-4f58-b538-017e4c0ec376

📥 Commits

Reviewing files that changed from the base of the PR and between 1d1d8e6 and 3ec376f.

📒 Files selected for processing (1)

• README.md

[coderabbitai]

🎯 Functional Correctness | 🟠 Major | 🏗️ Heavy lift

Align both README references with the actual formatter implementation.

The repository currently pins and invokes Oxfmt through its formatting configuration, so documenting Prettier is inaccurate. Either migrate the formatter implementation and dependencies to Prettier, or keep both README references pointed at Oxfmt until that migration is complete.

• README.md#L13-L13: restore the formatter description to match the current tooling.
• README.md#L24-L24: restore the rs fmt attribution or update the implementation first.

📍 Affects 1 file

• README.md#L13-L13 (this comment)
• README.md#L24-L24

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@README.md` at line 13, Update README.md lines 13-13 and 24-24 to reference
Oxfmt consistently with the current formatter configuration and rs fmt
implementation; do not document Prettier unless the formatter implementation and
dependencies are migrated first.