Add integration tests for absolute path validation in mount specifications

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

Author: Copilot

internal/config/config_test.go

@@ -802,6 +802,26 @@ func TestLoadFromStdin_InvalidMountFormat(t *testing.T) {
 			mounts:   `["/host::ro"]`,
 			errorMsg: "validation error",
 		},
+		{
+			name:     "relative source path",
+			mounts:   `["relative/path:/container:ro"]`,
+			errorMsg: "mount source must be an absolute path",
+		},
+		{
+			name:     "relative destination path",
+			mounts:   `["/host:relative/path:ro"]`,
+			errorMsg: "mount destination must be an absolute path",
+		},
+		{
+			name:     "dot relative source",
+			mounts:   `["./config:/app/config:ro"]`,
+			errorMsg: "mount source must be an absolute path",
+		},
+		{
+			name:     "dot relative destination",
+			mounts:   `["/host/config:./config:ro"]`,
+			errorMsg: "mount destination must be an absolute path",
+		},
 	}
 
 	for _, tt := range tests {