Restore pasting and rename sections to workspaces

Replacing the main menu dropped the Edit menu that AppKit routes
Cmd+V/C/A/Z through, so the composer could not paste at all. The menu is
rebuilt with those items, which --diag now dumps so the wiring can be
checked without a keyboard.

Workspaces also gained an order: the Cmd+K switcher has up/down controls,
creating one opens a naming modal instead of prefilling the composer, and
the UI now says workspace throughout. The stored JSON keeps the original
`sections` keys so existing data and sync payloads stay valid.

README.md

@@ -7,7 +7,10 @@ to your work. Click anything to copy it back to your clipboard.
 - **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.
-- **Sections** — type `# Name` in the composer; Cmd+K switches sections.
+- **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
+  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.
@@ -25,7 +28,7 @@ to your work. Click anything to copy it back to your clipboard.
 | --- | --- |
 | Capture current selection | Left Shift ×2 (or Cmd+Shift+C) |
 | Show/hide panel | Right Shift ×2 (or Cmd+Shift+Space) |
-| Switch/create section | Cmd+K |
+| Switch/create workspace | Cmd+K |
 | Search | Cmd+F |
 | Focus composer | Cmd+N |
 | Sync settings | Cmd+, |