Fix missing overlays, multiselect UX, and language propagation

[afffe18]

Motivation

• Overlays configured in frames (coloredAreas, annotations) were not rendered on the plot and thus invisible in the plot view.
• Native select multiple controls made non-adjacent selection awkward and required Ctrl/Cmd, hurting usability for axis columns and whitelist keywords.
• The top-right UI language toggle changed only the toggle label instead of the editor labels, and newly added plot languages did not inherit existing labels/titles.
• Config version was exposed as an editable setting but should not be displayed in the user settings UI.

Description

• Render coloredAreas as filled polygon traces and convert annotations into Plotly layout annotations so overlays appear on the chart, adding AreaTrace and getPlotAnnotations helpers in src/components/PlotPage.tsx and including those traces/annotations in the returned plot data.
• Replace native multi-select boxes with compact checkbox lists (MultiSelectInput) used for axis columns and whitelist keywords, allowing non-adjacent selection without keyboard modifiers and deduplicating selections via Set in src/App.tsx.
• Rework UI language support by adding a UI_LABELS dictionary and t() helper, wiring the top-right toggle to update visible labels/buttons and making many field labels use t(...) in src/App.tsx.
• Improve plot-language propagation in updateLanguages so new plotLanguages inherit existing values for frame titles, dataframe legendTitle, and axis labels instead of creating empty entries, and remove the user-editable Config version field from the settings UI.

Testing

• Ran npm run lint and it completed successfully.
• Ran npm run build (TypeScript compile + Vite build) and it completed successfully producing the production build.

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Codex Task