fix(issues): board polish — blocked column, drag fix, comment perms, task cleanup

- Add "blocked" to STATUS_ORDER/ALL_STATUSES and board visible columns
- Add min-h-[200px] to droppable columns for reliable empty-column drops
- Fix card click-vs-drag conflict with pointer-events-none on Link
- List view uses STATUS_ORDER from config instead of hardcoded order
- Create Issue dialog: add AssigneePicker for assigning on creation
- Issue detail page syncs from global useIssueStore for real-time updates
- Comment UpdateComment/DeleteComment: add author-or-admin permission check
- DeleteIssue: cancel running agent tasks before deletion

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/internal/handler/issue.go

@@ -458,6 +458,8 @@ func (h *Handler) DeleteIssue(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	h.TaskService.CancelTasksForIssue(r.Context(), issue.ID)
+
 	err := h.Queries.DeleteIssue(r.Context(), parseUUID(id))
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "failed to delete issue")