fix(onboarding): retire onboarding use case feature flag and prevent crash and redirect loop on use-case selection page

[MattBro]

Problem

This addresses this ticket where clicking the PostHog logo during onboarding caused a crash—the URL path /onboarding/use-case was being misinterpreted as a product key rather than a scene route.

When navigating to the use-case selection onboarding page, users experienced a crash and redirect loop. This happened because:

1. UseCaseSelection.tsx imported onboardingLogic, which mounted its urlToAction
2. urlToAction matched /onboarding/use-case with productKey = "use-case"
3. Since "use-case" isn't a valid product, availableOnboardingProducts["use-case"] returned undefined
4. The setProduct reducer returned undefined, violating Redux rules
5. onboardingLogic redirected to / since no valid product was found
6. sceneLogic redirected back to /onboarding/use-case, creating an infinite loop

Changes

• Remove onboardingLogic dependency from UseCaseSelection.tsx to prevent the urlToAction from matching on this page
• Add null coalescing to setProduct reducer to prevent undefined returns
• Remove the ONBOARDING_USE_CASE_SELECTION feature flag entirely - ship use-case selection as the default onboarding entry point for all users
• Update MinimalNavigation logo link to go to use-case selection when user hasn't completed onboarding
• Maintain proper else if chain in sceneLogic redirect logic to prevent incorrect redirects when team is unavailable

How did you test this code?

• Manually tested navigating to /onboarding/use-case directly
• Verified no redirect loop occurs
• Verified the "Skip onboarding" button still works correctly
• Tested that use-case selection flows to products page correctly

🤖 Generated with Claude Code

[github-actions[bot]]

Size Change: -314 B (-0.01%)

Total Size: 3.7 MB

ℹ️ View Unchanged

Filename	Size	Change
frontend/dist/toolbar.js	3.7 MB	-314 B (-0.01%)

_{compressed-size-action}

[posthog-bot]

Visual regression: Storybook UI snapshots updated

Changes: 6 snapshots (6 modified, 0 added, 0 deleted)

What this means:

• Snapshots have been automatically updated to match current rendering
• Next CI run will switch to CHECK mode to verify stability
• If snapshots change again, CHECK mode will fail (indicates flapping)

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