Coop: lock combat actions for the full duration of an active run

Players in a co-op were getting their combat action back every midnight
reset and offered the dungeon option in the morning DM. Per spec they
should be "off in the Co-op" and unable to also solo-grind dungeons.

Fix at the DB layer (so all CanDoCombat() paths agree):
- New helper lockCoopCombatActions() sets combat_actions_used=99 for any
  user in an active coop run. Called immediately after every
  resetAllAdvDailyActions() — at startup and at midnight.
- Render layer: morning DM now shows "combat locked (in Co-op #N, day
  X/Y)" and replaces the dungeon section with an explanatory line
  pointing them at !coop status.

Combat returns to normal automatically once the run completes/wipes —
the next midnight reset finds status != 'active' and skips the lock.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/plugin/coop_dungeon_db.go

@@ -172,6 +172,23 @@ func completeCoopRun(runID int, status string, reward int) error {
 	return err
 }
 
+// lockCoopCombatActions sets combat_actions_used to a value that exceeds the
+// holiday cap on every active co-op participant. Called after the midnight
+// reset (which would otherwise zero them) and at bot startup. Combat stays
+// locked for the full duration of the run — players in a co-op cannot also
+// solo-grind dungeons or arena.
+func lockCoopCombatActions() error {
+	d := db.Get()
+	_, err := d.Exec(`UPDATE adventure_characters
+		SET combat_actions_used = 99
+		WHERE user_id IN (
+			SELECT m.user_id FROM coop_dungeon_members m
+			JOIN coop_dungeon_runs r ON r.id = m.run_id
+			WHERE r.status = 'active'
+		)`)
+	return err
+}
+
 func setCoopRunInvitePostID(runID int, postID id.EventID) error {
 	d := db.Get()
 	_, err := d.Exec(`UPDATE coop_dungeon_runs SET invite_post_id = ? WHERE id = ?`, string(postID), runID)