Say "page", not "sheet", everywhere a user sees it

From the development repository at 854009c.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/host.md

@@ -118,7 +118,7 @@ Other options, all optional:
 ## Starting a session
 
 On the start screen, enter your name and the notebook for this session,
-and press **Start a session**.  You are on page 1, a blank sheet, and
+and press **Start a session**.  You are on page 1, blank, and
 **Session** in the toolbar shows the invitation.
 
 ### The notebook
@@ -172,8 +172,9 @@ page's width, at its natural size, in front of the images already
 there.  Natural size is the size the file records: a scan arrives at
 the size of the paper it came from.  A photo from a phone or camera
 records no useful size and arrives at a tenth of a millimetre per
-pixel.  An image wider than the page widens the page on both sides to
-hold it.  From there you move and scale it by hand, as described next;
+pixel.  An image wider than the page widens it on both sides, and one
+taller than the page lengthens it downward, so the whole image has room.
+From there you move and scale it by hand, as described next;
 there is no other setting to choose.  PNG and JPEG files are shared as
 they are unless very large; other formats, and images over 2400 pixels
 on a side or 1.5 MB, are converted to JPEG and reduced first, which
@@ -193,7 +194,7 @@ afterwards.  Only you and co-hosts can move images.
 
 For a page that begins with an image, press **New** and then **Image**.
 For a series of exercises, keep pressing **Image** on the same page: the
-sheet grows downward and everyone scrolls through them.  A new image does
+page grows downward and everyone scrolls through them.  A new image does
 not change anyone's zoom; it appears below, to be scrolled to.
 
 A tap of the eraser on an image removes it, whoever added it and
@@ -227,8 +228,8 @@ beside yours.  Only its owner can type in a box, as with any text.
 
 **Expand**, among the view buttons, makes the page fill your window for
 everyone, at your present zoom, in both directions: the quickest way to
-more room for writing around an exercise.  The sheet grows equally on
-every side, so nothing on the page moves.  The page keeps the new size
+more room for writing around an exercise.  The page grows equally on
+every side, so nothing on it moves.  The page keeps the new size
 in everyone's notebook.  **Shrink** is its opposite: the page becomes
 just large enough for everything on it, images and writing, with the
 margin of 5 mm around, which trims a page down to its exercise before you keep