Fix column order/widths and sizing in Hausmeister and GnuCash import

Hausmeister: reorder columns to Level, Fällig, Vorgang, Details. Level,
Fällig and Vorgang get a fixed width; only Details stretches to fill the
remaining space.

GnuCash-Import dialog: opens at 80% of the current monitor's size
(monitor-aware via the existing screeninfo-based helpers, not just the
raw/virtual screen size) instead of a fixed 960x640. In its booking
table, Import, Datum, Betrag and Status get a fixed width; Beschreibung
and Memo share the remaining space.

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

src/ccma/ui/gnucash_import_dialog.py

@@ -22,6 +22,7 @@ from ccma.services.gnucash_import import (
     list_transactions,
 )
 from ccma.storage.repository import MemberRepository, RepositoryError
+from ccma.ui.monitors import centered_geometry, preferred_monitor
 
 
 class GnuCashImportDialog(tk.Toplevel):
@@ -55,7 +56,8 @@ class GnuCashImportDialog(tk.Toplevel):
 
         self.title("Zahlungen aus GnuCash importieren")
         self.transient(master.winfo_toplevel())
-        self.geometry("960x640")
+        monitor = preferred_monitor(master.winfo_toplevel())
+        self.geometry(centered_geometry(round(monitor.width * 0.8), round(monitor.height * 0.8), monitor))
         self.minsize(780, 480)
         self.protocol("WM_DELETE_WINDOW", self.destroy)
         self.bind("<Escape>", lambda _event: self.destroy())
@@ -134,8 +136,8 @@ class GnuCashImportDialog(tk.Toplevel):
             ("status", "Status", 220),
         ):
             self.tree.heading(key, text=title)
-            self.tree.column(key, width=width, anchor="w")
-        self.tree.column("selected", anchor="center", stretch=False)
+            self.tree.column(key, width=width, anchor="w", stretch=key in {"description", "memo"})
+        self.tree.column("selected", anchor="center")
         self.tree.grid(row=0, column=0, sticky="nsew")
         scrollbar = ttk.Scrollbar(tree_frame, orient="vertical", command=self.tree.yview)
         scrollbar.grid(row=0, column=1, sticky="ns")