Fix right-click context menus firing their first item on Linux

Bound to <Button-3> with finally: menu.grab_release(), the menu lost its grab
immediately and the trailing <ButtonRelease-3> activated the entry under the
cursor — right-clicking a history row jumped straight into the edit dialog and
deleting was impossible.

- RIGHT_CLICK constant: <ButtonRelease-3> (<ButtonRelease-2> on macOS)
- history + queue menus built once on self, not per click
- drop the premature grab_release()

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/changelog.md

@@ -2,6 +2,15 @@
 
 Notable changes to the app. Newest first.
 
+## 2026-09-07 — fix: right-click context menu instantly triggered its first item
+
+On Linux the Tab 2 (and queue) right-click menu flashed and immediately ran
+"Bearbeiten" / "Löschen", so entries couldn't be deleted. Cause: the menu was
+bound to `<Button-3>` (press) and `finally: menu.grab_release()` dropped the
+grab, so the following `<ButtonRelease-3>` selected the item under the cursor.
+Fix: bind `<ButtonRelease-3>` (`<ButtonRelease-2>` on macOS), build each menu
+once, and drop the premature `grab_release()`.
+
 ## 2026-09-07 — map tiles → Esri (OSM 403s local files)
 
 The switch to `tiles="OpenStreetMap"` worked on the dev machine but the target