Substantial foundation upgrades

• Major components upgrades: Electron 42, Webpack 5, React 19, etc.
• Secure token storage https://github.com/hackjutsu/Lepton/issues/319
• More efficient memory management https://github.com/hackjutsu/Lepton/issues/465
• Bug fixes https://github.com/hackjutsu/Lepton/issues/539 https://github.com/hackjutsu/Lepton/issues/537 https://github.com/hackjutsu/Lepton/issues/532 New features
• All snippets/gists download + full content search https://github.com/hackjutsu/Lepton/issues/527 https://github.com/hackjutsu/Lepton/issues/254 https://github.com/hackjutsu/Lepton/issues/82 https://github.com/hackjutsu/Lepton/issues/208 https://github.com/hackjutsu/Lepton/issues/501 To enable full content download in .leptonrc.
• Built-in themes https://github.com/hackjutsu/Lepton/issues/541 https://github.com/hackjutsu/Lepton/issues/550 Supported values in .leptonrc's theme : light, dark, one-dark, atom-one-dark, github-light, github-dark, catppuccin-latte, catppuccin-mocha, solarized-light, solarized-dark, dracula, material-theme, ayu Example: dracula
• Internationalization(i18n) support https://github.com/hackjutsu/Lepton/issues/459 https://github.com/hackjutsu/Lepton/issues/331 https://github.com/hackjutsu/Lepton/issues/411
• Option tag.colored to enable colored tags https://github.com/hackjutsu/Lepton/issues/484
• Option startAtLogin to start at system startup https://github.com/hackjutsu/Lepton/issues/551
• Option window.closeToTray and window.minimizeToTray to minimize to tray https://github.com/hackjutsu/Lepton/issues/553