1d: Handle transactions in trapfalld digest + WebSocket broadcast

[ajianaz]

Parent: #231 · Blocked by: #236, #237

Scope

Wire transaction handling into the existing digest loop and WebSocket broadcast pipeline.

Changes

ServerMessage enum — add variant

pub enum ServerMessage {
    IssueCreated { issue: Issue },
    IssueUpdated { issue: Issue },
    EventReceived { issue_id: String, event_id: String },
    TransactionReceived { transaction_id: String, name: String, duration_ms: f64 }, // NEW
}

Digest loop — handle ParsedEnvelope.transactions

• After processing events, check if envelope has transactions
• Insert each transaction into DB via insert_transaction()
• Broadcast TransactionReceived to subscribed WebSocket clients for that project

Tasks

• Add TransactionReceived variant to ServerMessage
• In digest loop: iterate envelope.transactions after envelope.events
• Insert transaction to DB
• Broadcast WebSocket message
• Add error handling: log + skip on DB insert failure (don't drop events)
• Add test: mock envelope with transaction → verify DB insert + broadcast

Effort: ~2 hours