Polish pagination sizing and add Simic/Izzet/Gruul guild themes

[Terraphice]

Motivation

• Normalize the pagination page-number control so it visually matches the other pagination buttons.
• Add three missing guild theme families (Simic, Izzet, Gruul) with light/dark variants so they behave like existing guild themes in the site UI.

Description

• Changed the paginated page input to reuse the base button class by setting pageInput.className = "pagination-btn pagination-page-input" so it inherits consistent sizing and hover behavior.
• Adjusted page-input styles in styles/gallery.scss/styles/gallery.css to remove the oversized min-height and align typography/spacing with other pagination controls.
• Added simic, izzet, and gruul entries to THEME_FAMILIES and included them in MODE_THEME_OPTIONS in src/gallery/ui.js, wiring guild icons and resolved theme names to match the existing family implementation.
• Added light/dark theme token blocks for simic, izzet, and gruul to styles/themes.scss and the compiled styles/themes.css, using existing background assets and swapping accent colors between light/dark modes.

Testing

• Ran npm run lint and it completed without lint failures.
• Ran the project smoke/e2e tests via npm test (smoke test) and all automated checks passed: 57 passed, 0 failed.