Basking: live preview editing

Pages open in Live mode, where every line is rendered except the one being
edited, with Edit (plain markdown) and View (fully rendered) beside it.
Arrow keys, Backspace and Delete move between lines, code blocks are edited
as a whole, and edits are spliced back into the one text the rest of the
editor already saves.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

README.md

@@ -17,8 +17,10 @@ Named for the basking shark, which swims along with its mouth open and takes in
   Rename a page and every `[[link]]` to it is updated.
 - **Type `/` for commands**: headings, to-do lists, quotes, code blocks, dividers, today's date, the
   time. Lists continue when you press Enter and indent with Tab. Ctrl+B and Ctrl+I work as you expect.
-- **Write or Read.** Write shows the markdown; Read shows the page as it will look, with tasks you can
-  tick and links you can follow. Click a page in Read to start writing (Ctrl+E switches).
+- **Live, Edit or View.** Live is the default: every line shows rendered except the one you are on,
+  which shows its markdown, as in Obsidian's live preview. Edit shows the whole page as plain
+  markdown, and View shows the whole page rendered, with tasks you can tick and links you can follow.
+  Click a page in View to start writing. Ctrl+E switches between editing and View.
 - **Quick find with Ctrl+K** searches titles and text as you type, and makes a new page if there is no
   match.
 - **A journal.** Today opens the page for the day, with an Insert time button. Days link to each
@@ -169,7 +171,8 @@ lower-case letters, numbers and dashes). Restart Basking to see files added by h
 - Searching holds every page in memory, which is comfortable for tens of thousands of pages and not
   built for millions.
 - Pages are only reloaded from disk when Basking starts.
-- Write mode is plain markdown, not a block editor. Read mode shows how it looks.
+- Live preview works a line at a time (a code block counts as one), so a table or a quote spread over
+  several lines shows rendered line by line. View shows the whole page as one.
 
 ## Design