Make original plots always use multi-plot layout

[chengzhuzhang]

• Add original_plots_multi flag to Parameters class
• Modify make_plot_pdfs to use multi-plot layout for original plots
• Change coupled_global to exclude original plots from interactive viewer
• Add special handling for original plots in index page

Now when make_viewer=True:

• Regular component plots use interactive viewer
• Original plots are always displayed as multi-plot PDFs
• Index page includes links to both interactive viewers and PDF files

🤖 Generated with Claude Code

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[forsyth2]

This commit is included in #16, so closing this PR.