Make the row checkbox select items instead of ticking them off

The checkbox was marking items done, but the intent was to gather items
and act on them: tick several, then right-click to copy, copy as a list,
move, merge or delete them all at once. Done is still available from the
same menu, it is just no longer what the checkbox does.

README.md

@@ -4,8 +4,9 @@ A native macOS app for keeping prompts and photos, in the spirit of
 [Copper](https://shadcn.com/copper) by shadcn: a floating panel that sits next
 to your work. Click anything to copy it back to your clipboard.
 
-- **Checklists by default** — every item has a checkbox, so a workspace doubles
-  as a to-do list; done items stay in place, dimmed and struck through.
+- **Checkbox to select** — every item has a checkbox; tick several and act on
+  them at once (copy, delete, move, merge). Clicking the row itself still
+  copies that item.
 - **Click to copy** — text notes go back as text, photos go back as images.
 - **Capture from anywhere** — select text in any app and tap **Left Shift twice**.
 - **Photos** — paste (Cmd+V), drag & drop, or add via the photo button.
@@ -13,9 +14,11 @@ to your work. Click anything to copy it back to your clipboard.
   the Cmd+K switcher (which opens a name modal); Cmd+K switches, and the
   up/down arrows in the switcher reorder them. (The code and the saved JSON
   still call these `sections` so existing data keeps working.)
-- **Copy as List / Copy as Lines** — Cmd+click to multi-select (Shift+click for
-  a range), then copy the selection as a numbered list or as plain
-  newline-separated text, from the selection bar or the right-click menu.
+- **Copy as List / Copy as Lines** — select with the checkboxes (or Cmd+click,
+  or Shift+click for a range), then copy the selection as a numbered list or as
+  plain newline-separated text, from the selection bar, the right-click menu, or
+  Shift+Cmd+C / Option+Cmd+C. The same menu deletes, moves or merges the
+  selection.
 - **Merge Notes, Mark as Done, Edit, Move To** — right-click any item.
 - **Search** — Cmd+F searches across all sections.
 - **Sync (optional)** — generate an 8-digit code (`1234-5678`) on one Mac and