Allow deleting claims, creating standalone payments, and add a donations tab

Claims could previously only be cancelled (stornieren), which blocks once a
payment is allocated. Add a hard delete that releases any linked
payments/credits back to being unallocated instead of destroying them.

Payments could only be created from within a claim, forcing immediate
allocation. Add a bare payment creation flow in the Zahlungen tab so
incoming transfers can be logged first and allocated later.

Add a per-member Spenden tab (donations, backed by a new donations list on
ContributionData) so amounts paid beyond the membership fee can be tracked
and existing free payments allocated to them.

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

src/ccma/ui/payment_dialog.py

@@ -2,6 +2,7 @@ from __future__ import annotations
 
 import tkinter as tk
 from collections.abc import Callable
+from datetime import date
 from decimal import Decimal, InvalidOperation
 from tkinter import messagebox, ttk
 
@@ -15,6 +16,77 @@ from ccma.domain.dates import date_input_hint, format_date_for_display
 from ccma.storage.repository import MemberRepository, RepositoryError
 
 
+class PaymentCreateDialog(tk.Toplevel):
+    """Records a payment without requiring it to be tied to a claim right away.
+    Useful for logging an incoming bank transfer as soon as it arrives; it can be
+    allocated to claims or donations afterwards."""
+
+    def __init__(
+        self,
+        master: tk.Misc,
+        repository: MemberRepository,
+        member_id: str,
+        on_saved: Callable[[], None],
+    ):
+        super().__init__(master)
+        self.repository = repository
+        self.member_id = member_id
+        self.on_saved = on_saved
+        self.title("Zahlung anlegen")
+        self.transient(master.winfo_toplevel())
+        self.resizable(False, False)
+        self.bind("<Escape>", lambda _event: self.destroy())
+        self.frame = ttk.Frame(self, padding=18)
+        self.frame.pack(fill="both", expand=True)
+        self.frame.columnconfigure(1, weight=1)
+        self.variables = {
+            "date": tk.StringVar(value=format_date_for_display(date.today().isoformat())),
+            "amount": tk.StringVar(),
+            "gnucash": tk.StringVar(),
+            "reference": tk.StringVar(),
+        }
+        fields = (
+            (f"Zahlungsdatum ({date_input_hint()})", "date"),
+            ("Zahlungsbetrag", "amount"),
+            ("GnuCash-ID (optional)", "gnucash"),
+            ("Referenz", "reference"),
+        )
+        for row, (label, key) in enumerate(fields):
+            ttk.Label(self.frame, text=label).grid(row=row, column=0, sticky="w", padx=(0, 12), pady=5)
+            ttk.Entry(self.frame, textvariable=self.variables[key], width=42).grid(
+                row=row, column=1, sticky="ew", pady=5
+            )
+        ttk.Label(
+            self.frame,
+            text=(
+                "Die Zahlung wird zunächst ohne Zuordnung gespeichert. Sie kann anschließend "
+                "einer Forderung oder Spende zugeordnet werden."
+            ),
+            style="Mono.TLabel",
+            wraplength=380,
+        ).grid(row=len(fields), column=0, columnspan=2, sticky="w", pady=(8, 0))
+        buttons = ttk.Frame(self.frame)
+        buttons.grid(row=len(fields) + 1, column=0, columnspan=2, sticky="e", pady=(16, 0))
+        ttk.Button(buttons, text="Abbrechen", command=self.destroy).pack(side="left", padx=(0, 8))
+        ttk.Button(buttons, text="Speichern", style="Accent.TButton", command=self._save).pack(side="left")
+        self.after_idle(self.grab_set)
+
+    def _save(self) -> None:
+        try:
+            self.repository.create_payment(
+                self.member_id,
+                payment_date=self.variables["date"].get(),
+                amount=self.variables["amount"].get(),
+                gnucash_transaction_id=self.variables["gnucash"].get(),
+                reference=self.variables["reference"].get(),
+            )
+        except RepositoryError as exc:
+            messagebox.showerror("Zahlung konnte nicht gespeichert werden", str(exc), parent=self)
+            return
+        self.destroy()
+        self.on_saved()
+
+
 class PaymentEditDialog(tk.Toplevel):
     def __init__(
         self,