chore: remove CODEOWNERS chassis and the code-owner review gate

The repo is a 2-person team where both maintainers own every path, so the
CODEOWNERS machinery (generated CODEOWNERS, roles yml, render script, the two
drift/hand-edit CI jobs) gated nothing real while adding friction: every PR
showed "Review required" and own-PRs merged only via admin/bypass override.

Remove the whole chassis and drop the review gate:
- delete .github/CODEOWNERS, codeowners-roles.yml, render-codeowners.py,
  the CODEOWNERS workflow, and docs/dev/codeowners.md
- branch-protection.json: drop the two CODEOWNERS required status checks,
  set require_code_owner_reviews=false and required_approving_review_count=0
  (CI checks are the gate; maintainers merge their own PRs once green)
- scrub CODEOWNERS references from AGENTS.md, docs indexes, branch-protection
  and ci docs, GOVERNANCE.md, and CONTRIBUTING.md

The policy change is inert until an admin runs scripts/apply-branch-protection.sh.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/branch-protection.json

@@ -1,27 +1,19 @@
 {
-  "_comment": "Branch protection policy for main. Applied via scripts/apply-branch-protection.sh. See docs/branch-protection.md for rationale. NOTE: bypass_pull_request_allowances.users must mirror the engineering owners in .github/codeowners-roles.yml — code owners merge their own PRs without a second review; non-owners still need a code-owner approval. (render-codeowners.py does NOT generate this list; keep it in sync by hand.)",
+  "_comment": "Branch protection policy for main. Applied via scripts/apply-branch-protection.sh. See docs/dev/branch-protection.md for rationale. CODEOWNERS was removed (2-person team where both maintainers own everything, so code-owner review added friction without value). Review is no longer code-owner-scoped and no approvals are required; the required CI status checks are the gate. Maintainers merge their own PRs once checks pass.",
   "required_status_checks": {
     "strict": true,
     "contexts": [
       "Classify Changes",
       "Check AGENTS.md Links",
-      "Test omnigraph-server --features aws",
-      "CODEOWNERS matches source",
-      "CODEOWNERS not hand-edited"
+      "Test omnigraph-server --features aws"
     ]
   },
   "enforce_admins": false,
   "required_pull_request_reviews": {
-    "dismissal_restrictions": {},
-    "dismiss_stale_reviews": true,
-    "require_code_owner_reviews": true,
-    "required_approving_review_count": 1,
-    "require_last_push_approval": false,
-    "bypass_pull_request_allowances": {
-      "users": ["ragnorc", "aaltshuler"],
-      "teams": [],
-      "apps": []
-    }
+    "dismiss_stale_reviews": false,
+    "require_code_owner_reviews": false,
+    "required_approving_review_count": 0,
+    "require_last_push_approval": false
   },
   "restrictions": null,
   "required_linear_history": true,