Fix viewport scrolling and compact navigation

[Dacaidi]

Summary

• lock document-level scrolling so the virtualized champion table cannot create a second page scrollbar
• keep Draft, Analysis, Builds, and dialogs on their intended independent scroll containers
• open the champion selector by default in compact layouts and return to it after choosing an empty team slot
• reset compact navigation to Champions when resizing from desktop layout
• label the compact navigation as Ally / Champions / Opponent
• enforce a 480x600 minimum desktop window size

Behavior preserved

• desktop keeps the existing three-column layout
• Draft Analysis still opens automatically after all ten champions are filled
• LCU synchronization no longer strands compact layouts on a team sidebar
• extremely narrow web layouts remain accessible with table-local horizontal scrolling

Validation

• bun typecheck
• bun run --filter @draftgap/frontend lint
• bun test apps/frontend/src (15 passed)
• bun run --filter @draftgap/frontend build
• Tauri CLI configuration check
• browser regression at 1600x850, 1280 to 1024 resize, 480x600 cold start, and 360px web layout
• verified one Draft scroll container, one Analysis scroll container, no document scroll, and no blank page at the bottom
• verified LCU-style ten-pick completion still opens Draft Analysis