feat(email): each account gets its own email, in its own zone (milestone 495)

Milestone 495 "Email goes to each account, in its own time zone", on the
operator's ruling (System 156): notifications go to each user, times in
their zone, defaults on, toggled per user or per role.

- users.notify_alerts / notify_report (migration 0036): None follows the
  role's default, notify.<kind>.<role> in settings, all on to start.
- mail.pick_recipients: active accounts that want the email and have an
  address mail can reach (an SSO placeholder like name@oidc is skipped and
  flagged), each in its own zone with no UTC beside it, then the Also send
  to addresses in their chosen zone with UTC beside. One copy per address,
  all over one SMTP connection.
- Alerts, the weekly report and the test email (to you, in your zone, plus
  the typed addresses) send that way. The save-time smtp.tz capture is gone.
- Notifications: a role × email table of defaults, who each email reaches
  and who can't be reached, and Also send to with its own zone, which starts
  as the first admin's to open the page.
- Account page: your address and your two switches. Users: an Emailed
  column, and an admin sets an account's switches on its page.
- The Alerts page counts the accounts it emails. zone_select macro and
  formatting.zones_by_region shared by Account and Notifications.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

steward/alerts/service.py

@@ -257,17 +257,19 @@ async def active_count(db) -> int:
     )).scalar_one()
 
 
-def notify_targets(smtp: dict, webhook: dict) -> list[str]:
+def notify_targets(smtp: dict, webhook: dict, accounts: int = 0) -> list[str]:
     """Where an alert's notifications go, in words, by the same tests
     core.notifications.dispatch_notifications sends by: email when a server
-    and recipients are set, a webhook when its URL is. Empty: nobody (#5315)."""
+    is set and `accounts` (that get alerts) or Also send to addresses exist,
+    a webhook when its URL is. Empty: nobody (#5315, milestone 495)."""
     from urllib.parse import urlsplit
     out = []
     recipients = smtp.get("recipients") or []
     if isinstance(recipients, str):
         recipients = [r.strip() for r in recipients.split(",") if r.strip()]
-    if smtp.get("host") and recipients:
-        out.append("email to " + ", ".join(recipients))
+    who = ([f"{accounts} account{'s' if accounts != 1 else ''}"] if accounts else []) + recipients
+    if smtp.get("host") and who:
+        out.append("email to " + ", ".join(who))
     if url := webhook.get("url"):
         out.append("a webhook to " + (urlsplit(url).hostname or url))
     return out