fix(app): gate notification server selection

[opencode-agent]

Summary

• gate notification state selection on the shared connected-server registry
• fall back to the active or first registered server without blocking startup
• automatically select the preferred route server once its connection registers
• keep the behavior connection-type agnostic with no WSL-specific handling

Fixes #37481

Checks

• bun typecheck (packages/app)
• bun test --preload ./happydom.ts ./src/context/server.test.ts (12 passed)
• bun run test:unit (622 passed; existing i18n parity failure for five missing Arabic keys)
• bun x prettier --check packages/app/src/context/notification.tsx

Requested by: @Hona (Luke Parker via Slack)