fix(launcher): normalize rofi prompt spacing

- Add formatRofiPrompt to trim trailing whitespace and append a single space, keeping the prompt from running into the input field
- Apply it across all rofi -p usages in picker.ts and history-command.ts
- Add tests for formatRofiPrompt edge cases (empty/whitespace-only prompts)

changes/rofi-prompt-spacing.md

@@ -0,0 +1,4 @@
+type: fixed
+area: launcher
+
+- Rofi menu prompts now keep a space between the prompt text and the input field instead of running into the search placeholder.