chore: Introduce CODEOWNERS for path-based reviewer routing

[rapsealk]

resolves #11466

Summary

Adds .github/CODEOWNERS so PRs auto-request reviewers from @lablup/core_dev. The file is advisory only — it is not wired into branch protection, so CODEOWNERS approval is not required to merge.

Variant shipped here (Variant A — team handle)

*    @lablup/core_dev

Chosen because the team's current membership precisely matches the active human reviewer pool observed across the last 50 merged PRs — achimnol, jopemachine, HyeockJinKim, fregataa, seedspirit. So this is not a theoretical option; it is a precise codification of who already reviews PRs here.

Alternative considered (Variant B — individual handles)

For reference and discussion. Not what this PR ships:

*    @achimnol @HyeockJinKim @jopemachine @fregataa @seedspirit

	Variant A (team) — shipped	Variant B (individuals)
Stable across personnel changes	✅ (re-member the team)	❌ (edit the file)
Round-robin auto-request to one reviewer	✅ (if Code review assignment enabled on team)	❌ (all 5 always requested)
Visible to non-org viewers	Team page may not be	Names always visible
Works as a future branch-protection gate	✅	Awkward (per-person approval)

If reviewers prefer Variant B, the change is one line.

Important pre-merge check

This PR assumes Code review assignment is enabled on @lablup/core_dev (Settings → Members → Code review assignment, with round-robin or load-balance). Otherwise every PR will auto-request all 5 members, multiplying notification volume. Please verify before merging — and if not enabled, either turn it on or switch to Variant B.

Out of scope

CODEOWNERS does not replace existing labeler/dependabot workflows. Those stay as-is.

Test plan

• Confirm Code review assignment is enabled on @lablup/core_dev
• After merge, open a small test PR and verify a core_dev member is auto-requested
• Confirm GitHub UI shows no "Unknown owner" warnings on the file

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Note for reviewers: Graphite MCP wasn't available in the agent session, so this branch was opened with plain git push. Happy to re-stack via gt if preferred.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR introduces repository-wide CODEOWNERS metadata so GitHub can auto-request reviews from @lablup/core_dev, aligning reviewer routing with the project's current maintainer workflow described in issue #11466.

Changes:

• Add .github/CODEOWNERS with a default catch-all owner for all paths.
• Document the change in a Towncrier news fragment under changes/.
• Add inline rationale/comments explaining the intended advisory use of CODEOWNERS.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
.github/CODEOWNERS	Adds the repository-wide default owner mapping to auto-route PR reviews.
changes/11466.misc.md	Adds the release-note fragment describing the new CODEOWNERS setup.

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[jopemachine]

Is this something that was discussed previously? Also, I’d prefer that reviewers are not assigned while the PR is in draft—does it behave that way?

[rapsealk]

Is this something that was discussed previously?

No.

Also, I’d prefer that reviewers are not assigned while the PR is in draft—does it behave that way?

Yes - https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners#about-code-owners