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

README.md

@@ -1,8 +1,8 @@
 # action/check-naming
 
 Composite Gitea Action that validates a pull request's branch, title, Bug
-tracking, and AI authorship against the fritzlab Git standard. The current
-action fails (exits 1) on any violation; `@v1` is the legacy warn-only release
+tracking, PR-description AI authorship, and commit range against the fritzlab
+Git standard. The current action fails (exits 1) on any violation; `@v1` is the legacy warn-only release
 (Bugs program: see
 [fritzlab/agenthub#557](https://code.fritzlab.net/fritzlab/agenthub/issues/557)).
 
@@ -91,10 +91,12 @@ The check validates four things for every non-break-glass Agent PR:
    `<h2>` sections outside collapsed `<details>` content. Fenced, commented,
    scripted, or collapsed copies do not satisfy the visible provenance contract.
 
-4. **Commit attribution** — every commit in `base-sha..head-sha`, including
-   commits on `chore/` branches, ends with
-   the canonical `Authored-By` trailer, separated from the message body by a
-   blank line. The naming job must check out full history before this action.
+4. **Commit range** — `base-sha` and `head-sha` must identify available commits,
+   and `base-sha..head-sha` must contain at least one PR commit.
+   The naming job must check out full history before this action.
+   Attribution is required only in the PR description; commit messages are not
+   inspected. Existing commit trailers remain valid history, but no trailer is
+   required for a new commit.
 
 Every violation prints a `FAIL[check-naming]: ...` line and the step
 exits 1. To make the check required on a repo: drop any
@@ -103,7 +105,7 @@ context to the repo's `status_check_contexts` in agenthub `hub/hub.yaml`.
 
 ## Versions
 
-- unreleased — adds Bug tracking plus PR and commit attribution enforcement.
+- unreleased — requires Bug tracking and visible PR attribution, without commit-message watermarks.
 - `v2` — enforces branch and title naming.
 - `v1` — legacy warn-only: logs `WARN` lines, always exits 0.