Add contest follower notifications

[dylanjeffers]

Summary

Adds in-app + push delivery for two new contest notification types and expands the recipient set on existing contest notifications so contest followers (event subscribers) and host followers are first-class citizens.

Indexer (discovery-provider):

• comment.py writes remix_contest_update to event subscribers when the contest host posts a top-level comment on their event.
• track.py auto-subscribes the submitter to the contest event on create_track (skips if uploader is the host or already subscribed).
• utils.py includes contest subscribers in fan_remix_contest_started recipients.
• fan_remix_contest_ended.py, fan_remix_contest_ending_soon.py, fan_remix_contest_winners_selected.py: union in subscribers + host followers + parent-track savers; explicitly exclude the host (they have the artist_* counterparts).

Frontend (web + mobile + common):

• New RemixContestUpdate and FanRemixContestSubmission notification types in common, with adapter parsing both camelCase and snake_case keys (so this lands ahead of SDK regen).
• New web + mobile components, registered in Notification.tsx / NotificationListItem.tsx.
• Mobile navigation: RemixContestUpdate → contest entity, FanRemixContestSubmission → submitted remix track.

Test:

• Updated test_event_comment.py for the new entity_id / entity_user_id data shape.

Pairs with:

• api: Add contest follower notifications api#778 (SQL trigger + validator + swagger)
• pedalboard: Add contest follower push notifications pedalboard#11 (push processors)

Test plan

• After all three land, create a contest, submit a remix from a second account → submitter is auto-subscribed; host + any subscribers see fan_remix_contest_submission in-app and push
• Host posts a top-level comment on the event → subscribers see remix_contest_update in-app and push; host's own replies do NOT trigger it
• Subscribe to a contest from a third account → see fan_remix_contest_started (if unlisted→public happens after subscribing), _ending_soon, _ended, and _winners_selected in addition to remixers/host followers/savers
• Verify host does not receive the fan_* versions of ended / ending_soon / winners_selected

🤖 Generated with Claude Code

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