Add Amplitude analytics to contest UI

[dylanjeffers]

Summary

Adds Amplitude tracking for three key contest interactions, following the existing Remix Contest: event prefix and { remixContestId, trackId } property shape used by the host / pick-winners events.

Event	Fires when
REMIX_CONTEST_VIEW (Remix Contest: View)	Contest page/screen first resolves both trackId and eventId. Ref-guarded so re-renders (followers count, scroll-y reactions) don't re-fire.
REMIX_CONTEST_ENTER (Remix Contest: Enter)	User taps the Enter Contest / Upload Remix button. Wraps the existing useEnterContest callback so the upload flow itself is unchanged.
REMIX_CONTEST_VIEW_SUBMISSIONS (Remix Contest: View Submissions)	User opens the submissions tab.

Files

• packages/common/src/models/Analytics.ts — three new Name enum entries, three matching event-property types, and three union additions.
• packages/web/src/pages/contest-page/components/desktop/ContestPage.tsx — view effect, wrapped enter handler, submissions-pill onClick event.
• packages/mobile/src/screens/contest-screen/ContestScreen.tsx — view effect + wrapped enter handler.
• packages/mobile/src/screens/contest-screen/tabs/ContestSubmissionsTab.tsx — submissions-tab focus event.

Notes

• Mobile submissions firing uses useFocusedTab from react-native-collapsible-tab-view. The contest tab navigator runs with lazy: false, so a plain mount effect would fire even for users who only ever look at the Details tab.
• The ENTER event fires on click intent — i.e. before useRequiresAccountCallback redirects unauthenticated users to sign-in. This matches typical click-tracking semantics; switch to firing inside the gate if we want completion-only.

Test plan

• npm run typecheck passes (verified locally on @audius/common, @audius/web, @audius/mobile)
• Web: open a contest page → check Amplitude debug logs for one Remix Contest: View. Click Enter Contest → one Remix Contest: Enter. Click Submissions tab → one Remix Contest: View Submissions (and only one when toggling back and forth).
• Mobile: navigate to a contest screen → one Remix Contest: View. Tap Enter Contest → one Remix Contest: Enter. Swipe/tap to Submissions → one Remix Contest: View Submissions; swipe back and forth shouldn't re-fire.
• Confirm remixContestId + trackId payloads land in Amplitude alongside the existing remix-contest events.

🤖 Generated with Claude Code

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