fix(agents): strip banned Co-Authored-By trailer from bugfixer/feater/hotfixer templates

Completes job9/5a3de92 (which only cleaned commit-changer). These 3 execution
agents still emitted the banned trailer into their commit-message templates;
the settings.attribution backstop does not filter agent-authored message bodies.
Extended sweep of agents/ lib/ hooks/ templates/ for Co-Authored-By|Claude-Session|
--trailer now returns zero. Review finding A1 (BLOQUANT), J4-16 follow-up.

agents/bugfixer.md

@@ -180,8 +180,6 @@ Apply the fix following the plan:
 
    <what was wrong and why>
    <what the fix does>
-
-   Co-Authored-By: Claude <noreply@anthropic.com>
    ```
 7. Print summary:
    ```

agents/feater.md

@@ -138,8 +138,6 @@ Commit using conventional format:
 feat(<scope>): <what was added>
 
 <brief description of the feature>
-
-Co-Authored-By: Claude <noreply@anthropic.com>
 ```
 
 If the feature touched multiple concerns (e.g., feature + config +

agents/hotfixer.md

@@ -132,8 +132,6 @@ Apply the minimal change that fixes the bug:
 4. Commit using conventional format (only after verify AND security pass):
    ```
    fix(<scope>): <what was wrong>
-
-   Co-Authored-By: Claude <noreply@anthropic.com>
    ```
 5. Print summary:
    ```