Fix branch/commit view bugs

- Filter out non-branch refs (like HEAD) from branch list
- Walk all branch tips in commit list so older checkouts still
  show newer commits
- Show '(current)' instead of Checkout button for HEAD commit
- Swap nav link order in blob view (commits first, then tree)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/main/resources/templates/blob.html

@@ -7,9 +7,9 @@
 <h2 th:text="${filePath}">file.txt</h2>
 
 <p>
-<a th:href="@{/repo/{name}/tree/{hash}(name=${name}, hash=${hash})}">&lt; Back to tree</a>
-|
 <a th:href="@{/repo/{name}/commits(name=${name})}">&lt; Back to commits</a>
+|
+<a th:href="@{/repo/{name}/tree/{hash}(name=${name}, hash=${hash})}">&lt; Back to tree</a>
 </p>
 
 <table border="0" cellpadding="4" cellspacing="0">

src/main/resources/templates/commits.html

@@ -25,7 +25,8 @@
 <td th:text="${c.date}"></td>
 <td><a th:href="@{/repo/{name}/tree/{hash}(name=${name}, hash=${c.hash})}">Browse</a></td>
 <td>
-<form method="post" th:action="@{/repo/{name}/checkout-commit(name=${name})}">
+<span th:if="${c.hash == headHash}">(current)</span>
+<form th:unless="${c.hash == headHash}" method="post" th:action="@{/repo/{name}/checkout-commit(name=${name})}">
 <input type="hidden" name="hash" th:value="${c.hash}">
 <input type="submit" value="Checkout">
 </form>