Add configurable e-mail delivery: direct SMTP send or IMAP drafts

Mahnungs- and SEPA-info-mails could previously only be saved as a local .eml
file that still had to be manually imported into Thunderbird. Add a per-store
"E-Mail-Versand" configuration (Optionen -> E-Mail-Versand, stored in
repository.json alongside the rest of the club's settings, since different
stores may use different mailboxes) with four delivery modes:

- "Lokal speichern": today's behaviour, unchanged default for existing stores.
- "Direkt versenden": sends via SMTP.
- "Als Entwurf ablegen": IMAP APPENDs into a configurable drafts folder, so it
  shows up live in whatever mail client is already watching that account.
- "Jedes Mal fragen": prompts once per generation action (not per e-mail --
  a SEPA batch can cover dozens of members) with Senden/Entwürfe/Abbrechen.

New ccma.services.mail_delivery module (smtplib/imaplib, no new dependency)
opens one authenticated connection per batch and reuses it across all
messages instead of reconnecting per recipient. Both "Verbindung testen"
buttons in Options exercise the same connection path used for real delivery.
The archived per-member copy of every generated e-mail is unaffected and
still always written regardless of delivery mode.

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

src/ccma/ui/email_delivery_dialog.py

@@ -0,0 +1,68 @@
+from __future__ import annotations
+
+import tkinter as tk
+from tkinter import ttk
+
+from ccma.storage.repository import MemberRepository
+
+
+class EmailDeliveryChoiceDialog(tk.Toplevel):
+    """Shown once per generation action (not per individual e-mail) when the
+    repository's delivery mode is "ask" -- lets the board decide per-batch whether
+    to send immediately or park the e-mail(s) as a draft for later review."""
+
+    def __init__(self, master: tk.Misc, *, can_send: bool, can_draft: bool):
+        super().__init__(master)
+        self.result: str | None = None
+        self.title("E-Mail-Versand")
+        self.transient(master.winfo_toplevel())
+        self.resizable(False, False)
+        frame = ttk.Frame(self, padding=18)
+        frame.pack(fill="both", expand=True)
+        ttk.Label(
+            frame,
+            text="Wie soll mit dieser E-Mail verfahren werden?",
+            wraplength=360,
+            justify="left",
+        ).pack(anchor="w", pady=(0, 14))
+        buttons = ttk.Frame(frame)
+        buttons.pack(anchor="e")
+        ttk.Button(buttons, text="Abbrechen", command=self._cancel).pack(side="left", padx=(0, 8))
+        send_button = ttk.Button(buttons, text="Senden", command=self._choose_send)
+        send_button.pack(side="left", padx=(0, 8))
+        send_button.configure(state="normal" if can_send else "disabled")
+        draft_button = ttk.Button(
+            buttons, text="Als Entwurf ablegen", style="Accent.TButton", command=self._choose_drafts
+        )
+        draft_button.pack(side="left")
+        draft_button.configure(state="normal" if can_draft else "disabled")
+        self.bind("<Escape>", lambda _event: self._cancel())
+        self.protocol("WM_DELETE_WINDOW", self._cancel)
+        self.after_idle(self.grab_set)
+
+    def _choose_send(self) -> None:
+        self.result = "send"
+        self.destroy()
+
+    def _choose_drafts(self) -> None:
+        self.result = "drafts"
+        self.destroy()
+
+    def _cancel(self) -> None:
+        self.result = None
+        self.destroy()
+
+
+def resolve_delivery_mode(master: tk.Misc, repository: MemberRepository) -> str | None:
+    """Returns the delivery mode to use for the next generated e-mail(s): "local",
+    "send" or "drafts" -- or None if the board cancelled out of the "ask every time"
+    prompt, in which case the caller should abort without generating anything."""
+    settings = repository.get_email_settings()
+    mode = settings["delivery_mode"]
+    if mode in {"local", "send", "drafts"}:
+        return mode
+    dialog = EmailDeliveryChoiceDialog(
+        master, can_send=bool(settings["smtp_host"]), can_draft=bool(settings["imap_host"])
+    )
+    master.wait_window(dialog)
+    return dialog.result