feat(ui): unify themes and polish mobile navigation

[jouwdan]

Meith's themes, control panels, and plugin pages used inconsistent controls and mobile navigation. This change establishes shared UI primitives and applies them throughout the board so spacing, typography, touch targets, forms, and navigation behave consistently.

• Extend @meith/ui with page headers, shared control and surface recipes, scrollable navigation tabs, password visibility controls, and reusable navigation drawers. Expose shared UI through the plugin kit and adopt it in Calendar and Dues.
• Polish forum listings, reading views, search, authentication, account forms, and control panels while retaining each theme's visual identity.
• Put the mobile hamburger in the top bar across all five themes. Main and panel menus open from the right, expose expandable sub-sections, and support outside-tap, Escape, and close-button dismissal without JavaScript. Panel menus highlight the active destination; horizontal tabs reveal the active tab on load and resize.
• Update the theme and plugin documentation, generated reference, browser regressions, and populated-demo screenshot tour.

Validation:

• pnpm verify passed: 511 test files and 8,888 tests passed; 27 tests skipped.
• Production E2E build passed.
• 26 focused browser checks passed, covering all five themes, responsive layouts, drawer interactions with JavaScript enabled and disabled, active-tab scrolling, password controls, and touch targets.
• Populated-demo screenshot tour passed and screenshots were visually reviewed across themes, panels, and plugins.
• pnpm comments:check and git diff --check passed.

To regenerate the visual review, run pnpm exec playwright test --config=e2e/screenshot-ui-polish.config.ts after the E2E build. Screenshots and the local gallery are written to test-results/ui-polish/.