PIARC Toolkit — Dark Mode Persistence Fixes
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What changed
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1) Added a theme *bootstrap* inline script to each HTML page so the saved theme
   applies before CSS loads (prevents a flash of wrong theme).
2) Ensured `js/theme.js` is included on every page.
3) Normalized all scripts to use a single storage key: `piarc:theme` with
   backward-compatible reads from `piarc-theme` and `theme`.
4) Theme toggles now dispatch a `themechange` event so other components can
   sync immediately (e.g., sidebar).

Files updated
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HTML: admin-login.html, admin.html, feedback.html, index.html, tool1.html, tool2.html, tool6.html
JS:   app.js, layout.js, main.js

How to use
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- The user's choice persists automatically across pages and sessions.
- To toggle, call `window.Theme.toggle()` or set `document.documentElement.dataset.theme` and call `window.Theme.apply(theme)`.