Add a release-notes page linked from the footer version (v0.9.6)

Reconstructed from the commit history since the first production
deployment; the initial entry is the 0.9.0 port of the legacy bash
script to Kotlin/Spring Boot.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/main/resources/templates/fragments.html

@@ -37,7 +37,7 @@
 </div>
 
 <footer th:fragment="footer" class="site-footer">
-    <strong><em th:text="'GitTally v' + ${version}">GitTally</em></strong>
+    <strong><a href="/releases" title="Release notes"><em th:text="'GitTally v' + ${version}">GitTally</em></a></strong>
     — © <a href="https://michael.hoennig.de" target="_blank" rel="noopener noreferrer">Michael Hönnig</a>, 2026
     <th:block th:unless="${#strings.isEmpty(impressumUrl)}">
         — <a th:href="${impressumUrl}" target="_blank" rel="noopener noreferrer">Impressum (Legal Disclosure)</a>