feat(notify): bundled notifications, task watchers, daily summary

- Per-user routing (own mail / own Discord webhook) for task alarms
  (sent at once), shares, completed shared tasks and watched tasks;
  settings as JSON on the user (GET /auth/me, PATCH /auth/settings).
- Everything but alarms is queued and sent as one message per user
  after NOTIFY_DIGEST_MINUTES (default 5); mails now multipart with an
  HTML version, Discord as one embed. Three failed attempts drop it.
- Own changes never notify the actor, except on watched tasks when
  asked for; "paused" stops everything including alarms.
- Task watchers: POST/DELETE /tasks/{id}/watch, isWatching on tasks.
- Daily summary at a chosen time: overdue, today, tomorrow, plus the
  count of the next 7 days; nothing due, nothing sent.
- Migration 7; jobs do not run in the demo.

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

internal/domain/models.go

@@ -135,6 +135,67 @@ type User struct {
 	NotifyBeforeMinutes int      `json:"notifyBeforeMinutes"`
 	OrganizationID      string   `json:"organizationId,omitempty"`
 	CreatedAt           string   `json:"createdAt"`
+	// Only filled for the user's own profile (GET /auth/me, PATCH /auth/settings)
+	NotificationSettings *NotificationSettings `json:"notificationSettings,omitempty"`
+}
+
+// NotificationSettings: which events reach a user over which channel, the daily summary and a pause.
+type NotificationSettings struct {
+	Paused            bool               `json:"paused"`
+	IncludeOwnWatched bool               `json:"includeOwnWatched"`
+	Events            NotificationEvents `json:"events"`
+	DailySummary      DailySummary       `json:"dailySummary"`
+}
+
+type NotificationEvents struct {
+	Due      ChannelChoice `json:"due"`      // task alarms (sent at once)
+	Shared   ChannelChoice `json:"shared"`   // something was shared with me
+	TaskDone ChannelChoice `json:"taskDone"` // a shared task was completed
+	Watched  ChannelChoice `json:"watched"`  // a watched task changed
+}
+
+type ChannelChoice struct {
+	Email   bool `json:"email"`
+	Discord bool `json:"discord"`
+}
+
+type DailySummary struct {
+	Enabled bool   `json:"enabled"`
+	Time    string `json:"time"` // HH:MM, server time zone
+	Email   bool   `json:"email"`
+	Discord bool   `json:"discord"`
+}
+
+// DefaultNotificationSettings for users who never saved any; task alarms follow the old alarm channels.
+func DefaultNotificationSettings(alarmChannels []string) NotificationSettings {
+	due := ChannelChoice{}
+	for _, c := range alarmChannels {
+		due.Email = due.Email || c == "email"
+		due.Discord = due.Discord || c == "discord"
+	}
+	return NotificationSettings{
+		Events: NotificationEvents{
+			Due:     due,
+			Shared:  ChannelChoice{Email: true},
+			Watched: ChannelChoice{Email: true, Discord: true},
+		},
+		DailySummary: DailySummary{Time: "07:00", Email: true},
+	}
+}
+
+// Channels returns the choice for an event kind (due, shared, taskDone, watched).
+func (n NotificationSettings) Channels(kind string) ChannelChoice {
+	switch kind {
+	case "due":
+		return n.Events.Due
+	case "shared":
+		return n.Events.Shared
+	case "taskDone":
+		return n.Events.TaskDone
+	case "watched":
+		return n.Events.Watched
+	}
+	return ChannelChoice{}
 }
 
 type UserInvite struct {
@@ -167,6 +228,8 @@ type SubTask struct {
 }
 
 type Thought struct {
+	// IsWatching: the requesting user gets notified about changes (task watchers)
+	IsWatching     bool          `json:"isWatching,omitempty"`
 	ID             string        `json:"id"`
 	UserID         string        `json:"userId"`
 	Content        string        `json:"content"`