Toggleable multilingual inputs, remove dark-mode UI, and fix duplicate preview during batch export

[afffe18]

Motivation

• Make plot text fields (title, legend title, axis labels) reliably editable for all configured plot languages from a single control that can expand/collapse.
• Eliminate the app-level dark-mode controls and related runtime branches to simplify styling and enforce a single light UI.
• Prevent the first/backend preview from appearing twice when generating many plots (batch mode).

Description

• Update src/App.tsx to turn the current-language inputs into toggles by switching onFocus to onClick handlers and simplifying the visible field labels to a single top label (affects frame title, dataframe legendTitle, and axis label inputs).
• Remove dataframe/frame dark-mode controls and the Settings dark-mode toggle, remove the themeMode state path, and force a light color scheme in a useEffect that removes any dark class and sets color-scheme: light.
• Add isBatchMode state to src/components/PlotPage.tsx, set it while createPlots runs, and suppress the single-preview image when batch gallery mode is active to avoid duplicate display.
• Keep the colored-areas UI located below annotations in the frame editor (no change required to move it).

Testing

• Ran the full frontend build with npm run build (which runs tsc -b && vite build) and the build completed successfully.

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Codex Task