Require authorship only in PR descriptions (#11)

Remove commit-message watermark inspection while preserving visible PR attribution, naming, identity exemptions and nonempty commit-range validation.

All79 offline contract cases and shell syntax pass.

Ticket: https://agenthub.fritzlab.net/t-d12vqnp63v5d

check.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# Branch, PR body, and commit contract checker.
+# Branch, PR body, and commit-range contract checker.
 # v2: exits 1 on violation. Consumers that want warn-only set
 # continue-on-error: true on the job (or stay on @v1).
 set -euo pipefail
@@ -180,23 +180,9 @@ if [ "${BRANCH_KIND}" != "invalid" ]; then
       fi
     done
     if git cat-file -e "${BASE}^{commit}" 2>/dev/null && git cat-file -e "${HEAD}^{commit}" 2>/dev/null; then
-      commit_count=0
-      while IFS= read -r commit; do
-        [ -n "${commit}" ] || continue
-        commit_count=$((commit_count + 1))
-        message=$(git log -1 --format=%B "${commit}")
-        if ! printf '%s\n' "${message}" | awk '
-          { line[NR]=$0 }
-          END {
-            n=NR
-            while (n > 0 && line[n] == "") n--
-            if (n < 3 || line[n-1] != "" || line[n] !~ /^Authored-By: .+ \(.+\) <noreply@[[:alnum:].-]+>$/) exit 1
-          }
-        '; then
-          echo "FAIL[check-naming]: commit ${commit} must end with an Authored-By product/model trailer"
-          FAILED=1
-        fi
-      done < <(git rev-list --reverse "${BASE}..${HEAD}" 2>/dev/null)
+      # Attribution belongs only in the PR description, not commit messages.
+      # Keep the existing nonempty-range gate independently of message content.
+      commit_count=$(git rev-list --count "${BASE}..${HEAD}" 2>/dev/null) || commit_count=0
       if [ "${commit_count}" -eq 0 ]; then
         echo "FAIL[check-naming]: base-sha..head-sha contains no PR commits"
         FAILED=1