[agent-guidance] Fix relative links to STYLE.md and AGENTS.md

[pq]

🤖 Style guide fix-up using the review-tuner skill

See: flutter/dart-intellij-third-party#708

What changes

Section 3 of .gemini/styleguide.md links to STYLE.md and AGENTS.md. Because the style guide lives in .gemini/, those links resolve to .gemini/STYLE.md and .gemini/AGENTS.md, which don't exist. This PR points them at ../STYLE.md and ../AGENTS.md. No other text changes.

Why

• Deterministic: both targets exist at the repo root, and neither exists under .gemini/.
  These are the only relative links in the file.
• The file is also loaded by the local reviewing-devtools-prs skill, so agents and
  humans who follow the links currently land on a 404.
• Same class of bug as the wrong relative depth fixed in Add initial PR review skills and skill validation hooks. #9930.

No replay is needed; the links are broken regardless of review behavior.

Note

As far as we know, Gemini Code Assist reads only the style guide's own text and does
not open linked files. Key rules from STYLE.md/AGENTS.md may still need to be
restated in the style guide for the bot to apply them. That is not part of this PR.

Release notes

Style-guide-only change; no user-facing DevTools change. Needs the release-notes-not-required label (the PR template asks for it; the release-notes CI check only runs on .dart changes, so it won't block this PR).

Context: flutter/dart-intellij-third-party#708 ·
review-tuner skill

Prepared with an agent and reviewed by @pq.

Pre-launch Checklist

General checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read the Flutter Style Guide recently, and have followed its advice.
• I signed the CLA.
• I updated/added relevant documentation (doc comments with ///).

Issues checklist

• I listed at least one issue that this PR fixes in the description above.
• I listed at least one issue which has the contributions-welcome or good-first-issue label.
• I did not list at least one issue with the contributions-welcome or good-first-issue label. I understand this means my PR might take longer to be reviewed.

Tests checklist

• I added new tests to check the change I am making...
• OR there is a reason for not adding tests, which I explained in the PR description.

AI-tooling checklist

• I did not use any AI tooling in creating this PR.
• OR I did use AI tooling, and...
  • I read the AI contributions guidelines and agree to follow them.
  • I reviewed all AI-generated code before opening this PR.
  • I understand and am able to discuss the code in this PR.
  • I have verifed the accuracy of any AI-generated text included in the PR description.
  • I commit to verifying the accuracy of any AI-generated code or text that I upload in response to review comments.

Feature-change checklist

• This PR does not change the DevTools UI or behavior and...
  • I added the release-notes-not-required label or left a comment requesting the label be added.
• OR this PR does change the DevTools UI or behavior and...
  • I added an entry to packages/devtools_app/release_notes/NEXT_RELEASE_NOTES.md.
  • I included before/after screenshots and/or a GIF demo of the new UI to my PR description.
  • I ran the DevTools app locally to manually verify my changes.

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[gemini-code-assist]

Note

Gemini is unable to generate a review for this pull request due to the file types involved not being currently supported.