Rename Copy to Send and put it first in the row context menu

The main feature (copy selection to the other panel, F5) is now labeled
"Send" in the toolbar button, tooltips, and context menu across all 7
locales. Internal identifiers (copyToOtherPanel, ctx-copy, i18n keys)
and secondary strings (toasts, status bar, errors) are unchanged.
The context-menu entry moves ahead of Open/Edit as the first row item.
README, marketing site, and the Windows QA checklist updated to match.

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

docs/platform-notes.md

@@ -83,8 +83,9 @@ Code paths written blind (no Windows box was available); verify in order:
 5. External editor: default app opens via `cmd /c start`; the Choose… picker
    starts in Program Files and accepts an .exe; remote temp-edit → save →
    auto-upload works (directory watcher on NTFS).
-6. Context menus: Show in Explorer, Move to Recycle Bin (item restorable from
-   the bin), Copy Path; Permissions ABSENT on local rows, present on remote.
+6. Context menus: Send to Other Panel is the first row item; Show in Explorer,
+   Move to Recycle Bin (item restorable from the bin), Copy Path; Permissions
+   ABSENT on local rows, present on remote.
 7. Ctrl+T/W/F/S and Ctrl+digit tab jumps; tooltips read "Ctrl+…".
 8. connections.json ACL: `icacls connections.json` shows only the current
    user after saving a connection.