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/dev-notes.md

@@ -57,6 +57,20 @@ Lesson: a tile source that works from `curl` or an `http://` page can still fail
 from `file://`. Test the map by **opening the generated `karte.html` directly**,
 not just by checking the URL in the HTML.
 
+## Tk popup menus: bind `<ButtonRelease-3>`, not `<Button-3>` (2026-09-07)
+
+`widget.bind("<Button-3>", …)` + `menu.tk_popup(x, y)` + `finally:
+menu.grab_release()` is the Windows idiom and **misfires on X11**: `tk_popup`
+returns immediately, `grab_release()` drops the menu's grab, and the pending
+`<ButtonRelease-3>` then activates whatever entry is under the cursor (the first
+one). Symptom here: right-click a history row → menu flashes → edit dialog opens.
+
+Rules for this codebase:
+- bind the release event: `RIGHT_CLICK` constant (`<ButtonRelease-3>`, or
+  `<ButtonRelease-2>` on macOS),
+- build each context menu **once** (store on `self`), don't recreate per click,
+- just call `menu.tk_popup(...)` — no `grab_release()`.
+
 ## Nominatim query order matters
 
 `geocode_city` returns the **first** hit, trying PLZ-qualified first, then each