Add textlint to enforce writing guide

[jp-knj]

Description (required)

This PR adds and configures textlint to enforce the Astro Japanese writing guide for our documentation. It introduces a new prh.yml file with terminology rules (e.g., 標準表記の統一やコロン「：」の検出) and updates the .textlintrc.ja.json configuration to load those rules. contributors will receive automated feedback on terminology usage and formatting consistency in Japanese docs, reducing manual proofreading errors and ensuring a unified style.

📁 Directory Structure

.
├── .textlintrc.ja.json                ← (new) Textlint config for Japanese rules
├── package.json                       ← (modified) adds `lint:ja` script, textlint dependencies
└── src
    └── content
        └── docs
            └── ja
                └── …                  ← (existing) Japanese‐language MDX/MD files

Related issues & labels (optional)

• Closes: Add textlint CI to enforce Japanese translation style guide #11665
• Previous PR: Add textlint to enforce style guide #11691
• Suggested label: i18n

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[sarah11918]

Hi @jp-knj - I'm noticing that there are conflicts here that will need to be resolved.

Also, the open discussion seems to be ongoing, so I'm not sure what the status of this is, and what we need to go further with this. How will we know that we want this? Maybe the first step is at least to resolve the conflicts here?

[jp-knj]

Thank you for noticing the conflicts.
I’ve pushed a commit that should resolve them, but Not completely sure everything is in order.

When you have a moment, could you take a quick look and let me know if there’s anything else we need before merging?

I really appreciate your time, and I’m happy to make any updates. Thanks again!

[sarah11918]

Thanks @jp-knj ! Admittedly, I haven't been keeping up too much with the conversation in the Discussion #11665 as it seems Chris had some questions/comments. I think the next step is checking in with him there to make sure all his concerns are addressed!