Refactor config editor UI; add cross-tab sync and batch plot download/preview

[afffe18]

Motivation

• Improve the editor layout and controls for axis/layer selection and whitelist handling to match requested left/right grouping and inline toggles.
• Make frame title editing multilingual by expanding other-language inputs when focusing the active title.
• Prevent UI issues (darkmode grey panels, growing preview images) and add robust preview/create workflows and download options.
• Keep a single shared config across browser tabs and make resolution/tab-name behavior more predictable.

Description

• Reworked the multi-select component and usage so axis columns and layer whitelist lists show a header row with Select all / Deselect all, Expand / Collapse controls, and (for whitelist) a mode toggle inline; removed the old helper placeholder lines under those selectors, and applied the same header layout to axis controls. (edits in src/App.tsx)
• Reorganized layer card layout to group key settings (name/linewidth/alpha) and moved whitelist keyword management to its own block with expand/select controls and a mode toggle, and added per-layer expanded state. (edits in src/App.tsx)
• When the active-frame title input is focused the UI now expands to show title inputs for all other configured plot languages. (edits in src/App.tsx)
• Persist plot config to localStorage and listen for storage events so multiple tabs on the same device share and synchronize the same config; added loading of cached config on startup. (edits in src/App.tsx and src/utils/configIo.ts)
• Tightened resolution input handling to accept svg or a clamped integer between 30 and 999, and treat an empty numeric input as 0; fixed auto-tab-name collisions by escaping the dynamic regex prefix. (edits in src/App.tsx)
• Removed grey translucent backgrounds in dark mode for primary config sections to avoid visual artifacts by switching to transparent dark backgrounds. (edits in src/App.tsx, small CSS adjustments)
• Overhauled plot preview/download flow: top-level header buttons now trigger explicit preview current or create all actions, plot batching shows x of y Plots created progress, added a refresh button, and moved/added a single “Download all (.zip)” action in the Backend preview panel. (edits in src/App.tsx, src/components/PlotPage.tsx)
• Stabilized preview image sizing to avoid progressive width growth by using h-auto max-w-full, and removed redundant per-panel create/preview buttons. (edits in src/components/PlotPage.tsx)
• Implemented backend /api/download-plots which renders requested plots server-side and returns a ZIP archive of images, honoring export_file_name when present. (edits in backend/app.py)

Testing

• Ran lint with npm run lint, which completed successfully.
• Built the frontend with npm run build, which completed successfully.
• npm run test:frontend did not run to completion in this environment due to the Node runtime not supporting the repository's --test-isolation=none flag.
• npm run test:backend did not run in this environment because the test script expects a Windows virtualenv path that is not available here.

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Codex Task