Use semantic theme tokens for public changelog to fix dark mode contrast

Replaced hardcoded colors (e.g. bg-white, border-black, border-black/10) with semantic Tailwind tokens (bg-background, border-border, border-foreground) across the public changelog UI so the site respects the ThemeProvider and system/dark/light preferences.frontend
Updated visual elements including headers, footers, entry dividers, badges, tag buttons, and the empty-state panel to use the new semantic tokens for consistent theming.frontend

Fixed illegible or invisible elements in dark mode (backgrounds, borders, input borders, and divider lines) on public changelog pages so content is readable in all themes.frontend
Adjusted PasswordGate and error styling to use semantic colors (including destructive text and shadow color) for correct contrast in dark and light themes.frontend