Make the composer wrap and grow, and surface Launch at Login

Long prompts hit a single-line field before; the composer is now an
NSTextView that wraps and grows up to seven lines, keeps Return as send,
and uses Shift+Return for a newline. Launch at Login already existed in
the menu bar icon's right-click menu, so it is now also a toggle in the
sync panel where it is easier to find.

README.md

@@ -11,6 +11,10 @@ to your work. Select what you need and send it back to your clipboard.
   image.
 - **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.
+- **A composer that grows** — long prompts wrap and the input grows up to seven
+  lines, then scrolls. Return sends, Shift+Return inserts a newline.
+- **Launch at Login** — toggle in the sync panel (Cmd+,) or the menu bar icon's
+  right-click menu, to start Prompt on boot.
 - **Workspaces** — type `# Name` in the composer, or use "New Workspace" in
   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
@@ -33,6 +37,7 @@ to your work. Select what you need and send it back to your clipboard.
 | Switch/create workspace | Cmd+K |
 | Search | Cmd+F |
 | Focus composer | Cmd+N |
+| New line in composer | Shift+Return |
 | Sync settings | Cmd+, |
 | Copy selection as numbered list | Shift+Cmd+C |
 | Copy selection as plain lines | Option+Cmd+C |