fix(app): avoid shortcut settings flash

[opencode-agent]

Summary

• keep both settings dialogs controlled and wrap tab navigation in Solid's startTransition so the current tab remains painted while the next tab renders
• eagerly import the visible Shortcuts controls (ButtonV2, IconButtonV2, TextInputV2, and SettingsListV2) while leaving the conditionally rendered icon lazy
• merge current origin/dev while preserving upstream provider navigation

Validation

• bun typecheck (packages/app)
• bun x prettier --check for all three changed files
• git diff --check origin/dev
• Playwright at 1280x800 using the real app UI with mocked backend data
• Playwright navigated General, Shortcuts, Servers, Providers, and Models with 188 animation-frame samples and no blank frames or errors
• Synchronized before/after video

Comparison

• before: b44bc0ad0740afe80beae0a1981c2c4d96f67173
• after: 3bf3493b2240dbb5e1ba4928f68f7137200828d3