feat(dashboard): admin setting to choose which event kinds appear in the "next meeting" widget

[mindsers]

Context

The dashboard "Prochaine réunion" widget currently shows the next upcoming Event whose template is not a day off (see getNextMeeting in app/features/dashboard/server/dashboard.server.ts, which filters NOT: { template: { key: EventTemplateKey.DayOff } }). The visible template set is hard-coded.

Congregations differ on what should appear there:

• Some only want regular meetings (midweek-meeting, weekend-meeting).
• Some want the memorial or one-off events to appear too.
• Some have custom EventTemplate rows (field service meetings, elders' meetings, …) and want fine-grained control.

Proposal

Let an admin (Permission Admin or SettingsManager — TBD) configure which EventTemplates the widget surfaces.

UX sketch:

• New section in /settings (or under congregation settings): "Tableau de bord — Prochaine réunion".
• Multi-select of the congregation's EventTemplate rows. Default: all non-system templates.
• Persist as a Setting row (key = 'dashboard.nextMeeting.visibleTemplateKeys', value = JSON array of EventTemplate.key strings).

Technical notes:

• Reuse the existing Setting model + service. Setting has compound unique [key, congregationId] — remember to use findFirst({ where: { key } }), not findUnique (project gotcha).
• Store EventTemplate.key strings (stable per-congregation, survive template renames), not IDs.
• Filter the picker with !isSystemTemplate(key) (app/features/events/model/event-template.type.ts) — that excludes day-off (confidentiality guard from fix/event-widget) and freeform (arguably correct — freeform events shouldn't own the "next meeting" widget).
• getNextMeeting reads the setting and, when unset, falls back to "all non-system templates". Replaces the current hard-coded NOT DayOff filter.

Estimate

~half a day. The EventTemplate rename (#267) removed the EventKind enum this issue was originally written against; the setting is now trivially a list of template keys, and isSystemTemplate() already exists.

Out of scope

• Per-user preference (this is a congregation-wide setting).
• Reordering / multiple "next" cards.

Related

Related to the security fix on branch fix/event-widget that stopped the widget from leaking other users' days off.

[mindsers]

Progress since the issue was opened:

• The EventKind enum this issue was written against is gone — feat(events): rename Programme* models to Event*/Template* #267 replaced it with the per-congregation EventTemplate table (app/database/schema.prisma:669) plus an EventTemplateKey enum for the five system keys (app/features/events/model/event-template.type.ts:1).
• isSystemTemplate(key) (same file, line 19) already flags day-off and freeform as read-only system templates — a ready-made guard for the settings picker.
• getNextMeeting (app/features/dashboard/server/dashboard.server.ts:227) already filters on template rather than kind (NOT: { template: { key: EventTemplateKey.DayOff } }), so the fallback path is a one-line change.

Still not done:

• No Setting row for the picker.
• No settings UI section for "Prochaine réunion".
• getNextMeeting doesn't read the setting yet.

Net effect: the scope shrank from a ~1-day feature to a ~half-day one. Setting shape is now dashboard.nextMeeting.visibleTemplateKeys (JSON array of EventTemplate.key strings) — no ID migration, no enum work.