feat(analytics): add Chat Blast: Message Viewed event

[dylanjeffers]

What

Adds a new Amplitude analytics event, Chat Blast: Message Viewed, that fires when a user opens a DM thread that is a blast (chat.is_blast === true).

Previously the only blast recipient-side event was Chat Blast: CTA Clicked; there was no signal for a user actually opening the blast thread. This tracks opens.

Behavior

• Fires once per blast per user — not on every re-open. Dedup is keyed on the blast chat_id, persisted in localStorage (web) / AsyncStorage (mobile).
• Fires on both web (ChatPage) and mobile (ChatScreen), mirroring the existing track(make(...)) pattern used by CHAT_BLAST_MESSAGE_SENT.

Event properties

Property	Notes
isNativeMobile	false on web, true on mobile (existing convention)
chatId	The blast thread's chat_id (the recipient-side blast identifier; the client ChatBlast type has no separate blast_id)
audience	Blast audience type
audienceContentType	track / album when scoped to content
audienceContentId	Decoded via OptionalHashId.parse to a numeric ID, matching CHAT_BLAST_MESSAGE_SENT

Changes

• packages/common/src/models/Analytics.ts — add CHAT_BLAST_MESSAGE_VIEWED to the Name enum, add the ChatBlastMessageViewed type, and register it in the AllTrackingEvents union.
• packages/web/src/pages/chat-page/ChatPage.tsx — useEffect that fires the event on opening a blast thread, deduped via localStorage.
• packages/mobile/src/screens/chat-screen/ChatScreen.tsx — same, deduped via AsyncStorage.
• packages/mobile/src/constants/storage-keys.ts — new VIEWED_BLAST_CHATS_KEY.

Testing

• tsc typecheck passes for common, web, and mobile.
• eslint clean on all changed files.

🤖 Generated with Claude Code

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