chore: update CODEOWNERS to use protocol team (#384)

## Summary

- Update CODEOWNERS to use `@celestiaorg/protocol` team
- Remove `assign-random-reviewer.yml` workflow (no longer needed since
the protocol team's [review assignment
settings](https://github.com/orgs/celestiaorg/teams/protocol/edit/review_assignment)
auto-assign 1 reviewer per PR)

## Context

Part of
https://linear.app/celestia/issue/PROTOCO-1217/fix-codeowners-and-pr-reviews-for-protocol-maintained-repos

This was tested and works as expected on celestia-app which now has the
protocol team as CODEOWNERs and a PR auto-requested a review from Vlad:
celestiaorg/celestia-app#6875

Supersedes #383 (recreated with signed commits to allow auto-merge).

Closes
https://linear.app/celestia/issue/PROTOCO-1217/fix-codeowners-and-pr-reviews-for-protocol-maintained-repos

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: rootulp

.github/CODEOWNERS

@@ -1,10 +1,8 @@
-# CODEOWNERS: https://help.github.com/articles/about-codeowners/
+# CODEOWNERS: <https://help.github.com/articles/about-codeowners/>
 
-# Everything goes through the following "global owners" by default.
-# Unless a later match takes precedence, these three will be
-# requested for review when someone opens a PR.
-# Note that the last matching pattern takes precedence, so
-# global owners are only requested if there isn't a more specific
-# codeowner specified below. For this reason, the global codeowners
-# are often repeated in package-level definitions.
-* @celestiaorg/celestia-core @celestiaorg/celestia-node
+# Everything goes through the protocol team by default. The team's review
+# assignment settings control how many reviewers are auto-assigned per PR.
+# See: https://github.com/orgs/celestiaorg/teams/protocol/edit/review_assignment
+
+# global owners
+* @celestiaorg/protocol