Add Rollback Selected button to staging page

Rollback restores selected unstaged files to their HEAD state
using git checkout. The button shares the form with Stage Selected,
distinguished by the submit button's name/value pair.

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

src/main/java/be/seeseepuff/webgit/controller/RepoController.java

@@ -146,8 +146,12 @@ public class RepoController
 	}
 
 	@PostMapping("/repo/{name}/stage")
-	public String stage(@PathVariable String name, @RequestParam List<String> files) throws IOException, GitAPIException
+	public String stage(@PathVariable String name, @RequestParam List<String> files,
+						@RequestParam(defaultValue = "Stage Selected") String action) throws IOException, GitAPIException
 	{
+		if ("Rollback Selected".equals(action))
+			gitService.rollbackFiles(name, files);
+		else
 			gitService.stageFiles(name, files);
 		return "redirect:/repo/" + name + "/changes";
 	}

src/main/java/be/seeseepuff/webgit/service/GitService.java

@@ -266,6 +266,19 @@ public class GitService
 		}
 	}
 
+	public void rollbackFiles(String name, List<String> files) throws IOException, GitAPIException
+	{
+		try (Git git = openRepository(name))
+		{
+			var checkout = git.checkout().setStartPoint("HEAD");
+			for (String file : files)
+			{
+				checkout.addPath(file);
+			}
+			checkout.call();
+		}
+	}
+
 	public void commit(String name, String message) throws IOException, GitAPIException
 	{
 		try (Git git = openRepository(name))

src/main/resources/templates/changes.html

@@ -19,7 +19,8 @@
 </tr>
 </table>
 <br>
-<input type="submit" value="Stage Selected">
+<input type="submit" name="action" value="Stage Selected">
+<input type="submit" name="action" value="Rollback Selected">
 </form>
 <p th:if="${#lists.isEmpty(modifiedFiles)}"><i>No modified files.</i></p>
 

src/test/java/be/seeseepuff/webgit/controller/RepoControllerTest.java

@@ -139,6 +139,18 @@ class RepoControllerTest
 		verify(gitService).stageFiles("myrepo", List.of("a.txt", "b.txt"));
 	}
 
+	@Test
+	void rollbackRedirectsToChanges() throws Exception
+	{
+		mockMvc.perform(post("/repo/myrepo/stage")
+				.param("files", "a.txt")
+				.param("action", "Rollback Selected"))
+			.andExpect(status().is3xxRedirection())
+			.andExpect(redirectedUrl("/repo/myrepo/changes"));
+
+		verify(gitService).rollbackFiles("myrepo", List.of("a.txt"));
+	}
+
 	@Test
 	void unstageRedirectsToChanges() throws Exception
 	{

src/test/java/be/seeseepuff/webgit/service/GitServiceTest.java

@@ -451,4 +451,16 @@ class GitServiceTest
 		String diff = gitService.getWorkingTreeDiff("myrepo", "README.md");
 		assertTrue(diff.isEmpty());
 	}
+
+	@Test
+	void rollbackFilesRestoresContent() throws GitAPIException, IOException
+	{
+		gitService.cloneRepository(bareRemote.toUri().toString(), "myrepo");
+		Path readme = worktreePath.resolve("myrepo").resolve("README.md");
+		Files.writeString(readme, "modified");
+
+		gitService.rollbackFiles("myrepo", List.of("README.md"));
+
+		assertEquals("# Test", Files.readString(readme));
+	}
 }