docs: document Windows Terminal Shift+Enter limitation

Windows Terminal does not support the Kitty keyboard protocol, so
Shift+Enter cannot be distinguished from Enter. Document that users
should use Ctrl+Enter for multi-line input instead.

- Add Windows Terminal note in Terminal Setup section
- Update Keyboard Shortcuts table with Windows note
- Show Windows-specific hint in /hotkeys command

packages/coding-agent/src/modes/interactive/interactive-mode.ts

@@ -2485,7 +2485,7 @@ export class InteractiveMode {
 | Key | Action |
 |-----|--------|
 | \`${submit}\` | Send message |
-| \`${newLine}\` | New line |
+| \`${newLine}\` | New line${process.platform === "win32" ? " (Ctrl+Enter on Windows Terminal)" : ""} |
 | \`${deleteWordBackward}\` | Delete word backwards |
 | \`${deleteToLineStart}\` | Delete to start of line |
 | \`${deleteToLineEnd}\` | Delete to end of line |