Add a dashboard app for the figure

[macromeer]

Adds app/, a Shiny app where you can change the figure's settings and download the result. It uses the plotting functions from R/figure.R (#4), so the script and the app draw the same plots. Uploading your own data and deploying to GitHub Pages come in later PRs.

The app

• Sidebar: every setting from figure_defaults(), grouped by panel: font size, which panels to show, the two group colours, lognormal sigma and the inset/polygon switches (B), jitter seed and point opacity (C), the shear-stress constant and dashed lines (D), the decay constants and band width (E), and the viridis palette (F). A reset button restores the defaults. Invalid values (empty fields, a negative constant, no panel selected) show a message in place of the figure.
• Figure tab: preview at the script's fixed size (1148 × 686 px). Downloads: PNG at 96, 150 or 300 dpi (same layout, more pixels) and SVG.
• Panel tab: one panel at a larger size. It is drawn in its cell of the 3 × 2 layout and then trimmed, so it looks as it does in the figure (drawn alone, the insets in B and D would shift).
• About tab.

Each panel is cached and rebuilt only when one of its own settings changes. The colour pickers are native <input type="color"> elements with a small input binding, so no extra package is needed.

Shinylive (webR)

The plan is to host it on GitHub Pages with Shinylive, so R runs in the visitor's browser. I exported this branch with shinylive::export() and drove it in headless Chromium. It works:

• about 16 s from opening the page to the first figure (served from localhost), and 3–4 s per settings change;
• text uses webR's Noto Sans, so fonts differ slightly from the script's exports;
• the app avoids cairo devices, which crash in webR once magick is loaded, and passes an explicit cache to bindCache(), because Shinylive sets up no default one.

Tests and dependencies

• tests/testthat/test-app.R checks the server logic with shiny::testServer(): defaults, settings reaching the panels, panel selection, the validation messages, the panel tab, and both downloads (PNG pixel size per dpi). 91 tests pass locally.
• shiny, bslib and ragg are added to Suggests, so CI installs them. The script itself doesn't need them.
• README: new "Dashboard" section with how to run the app locally.

Run it locally with shiny::runApp("app").

🤖 Generated with Claude Code