Show loading screen before switch console is ready

[Pigbibi]

Summary

• show a dedicated loading screen while strategy/session/account config is loading
• hide the switch workspace until the app is ready
• add rolling progress motion with reduced-motion fallback
• add validation coverage for the boot loading shell

Validation

• jq empty web/strategy-switch-console/strategy-profiles.example.json
• node --experimental-default-type=module tests/strategy_switch_worker_validation.mjs
• sed -n '/<script>/,/</script>/p' web/strategy-switch-console/index.html | sed '1d;' | node --check --input-type=commonjs
• node --check --input-type=module < web/strategy-switch-console/page_asset.js
• node --check --input-type=module < web/strategy-switch-console/worker.js
• python3 scripts/runtime_settings.py validate
• python3 -m unittest discover -s tests -v