[Copilot]

Passing unconverted model output to save_all_plots() produces repeated downstream failures. Add shared validation to reject malformed input immediately with guidance to run convert_output().

• Validation: Internal check_data() requires a data frame containing label and estimate columns; accepts tibbles.
• Coverage: Call validation first in save_all_plots() and all standalone plot/table functions accepting dat. Leave utility files unchanged.

save_all_plots(list(label = "biomass", estimate = 1))
# Error: dat is not the appropriate format. Have you run `convert_output()`?

• Fixes check dat argument (and others) at the start of save_all_plots() #445