fix: feishu reply context truncation + task events NULL data crash (#508)

* fix(feishu): increase reply context max length from 500 to 2000

500 bytes is too short for CJK/Unicode text (each accented char = 2-3
bytes, so ~250 real characters). Increase to 2000 so reply context is
not aggressively truncated.

* fix(teams): handle NULL data column in task events queries

ListTaskEvents and ListTeamEvents crash with "unsupported Scan,
storing driver.Value type <nil> into type *json.RawMessage" when the
data column is NULL. Use COALESCE(data, '{}') to return an empty JSON
object instead.

---------

Co-authored-by: Luvu182 <208665161+Luvu182@users.noreply.github.com>

internal/channels/feishu/bot.go

@@ -277,7 +277,7 @@ func (c *Channel) handleMessageEvent(ctx context.Context, event *MessageEvent) {
 	}
 }
 
-const replyContextMaxLen = 500
+const replyContextMaxLen = 2000
 
 // fetchReplyContext fetches the parent message content and returns a formatted
 // reply context string + any downloaded media from the parent message.

internal/store/pg/teams_tasks_activity.go

@@ -132,7 +132,7 @@ func (s *PGTeamStore) RecordTaskEvent(ctx context.Context, event *store.TeamTask
 func (s *PGTeamStore) ListTaskEvents(ctx context.Context, taskID uuid.UUID) ([]store.TeamTaskEventData, error) {
 	tid := tenantIDForInsert(ctx)
 	rows, err := s.db.QueryContext(ctx,
-		`SELECT id, task_id, event_type, actor_type, actor_id, data, created_at
+		`SELECT id, task_id, event_type, actor_type, actor_id, COALESCE(data, '{}'), created_at
 		 FROM team_task_events
 		 WHERE task_id = $1 AND tenant_id = $2
 		 ORDER BY created_at ASC`, taskID, tid)
@@ -160,7 +160,7 @@ func (s *PGTeamStore) ListTeamEvents(ctx context.Context, teamID uuid.UUID, limi
 	}
 	tid := tenantIDForInsert(ctx)
 	rows, err := s.db.QueryContext(ctx,
-		`SELECT e.id, e.task_id, e.event_type, e.actor_type, e.actor_id, e.data, e.created_at
+		`SELECT e.id, e.task_id, e.event_type, e.actor_type, e.actor_id, COALESCE(e.data, '{}'), e.created_at
 		 FROM team_task_events e
 		 JOIN team_tasks t ON t.id = e.task_id
 		 WHERE t.team_id = $1 AND t.tenant_id = $4