morgul pedestal: work on primary data, do not require VDS to merged.h5

i.e. default is to acquire 4x½ module data sets but code still assumes 2x1 module, which we hacked by making a VDS but would be good to have `morgul pedestal` recognise the primary data

從 `morgul pedestal` 入口點開始，追蹤它如何選取輸入資料以及如何要求 `merged.h5`。比較預設的 4×½-module primary data 與假定的 2×1-module 配置。完成的標準是命令能夠直接辨識 primary data，而不要求 VDS。

由索引模型根據 Issue 內容生成。