feat: epoch detail claimed/unclaimed, closed webhook, comparison & projection

[Yilkash]

Summary

Implements all 4 assigned epoch-related issues:

#818 — Add claimed/unclaimed totals to epoch detail

• now returns and fields
• = sum of and events
• = (never negative)
• Acceptance criteria:

#819 — Fire epoch.closed webhook when all yield is claimed

• Adds column to table (migration 030)
• After each yield claim, the indexer checks if
• If so, sets (idempotent — fires at most once per epoch)
• Emits webhook with
• Re-processing the same event does not re-fire the webhook

#820 — Add epoch comparison endpoint

• Returns both epochs side-by-side with: yieldAmount, totalShares, yieldPerShare, distributedAt, participationRate
• Includes delta: { yieldAmount, yieldPerShare } (b minus a)
• Returns 404 if either epoch does not exist

#821 — Add next epoch projection endpoint

• Returns { estimatedYieldAmount, estimatedDistributionDate, basedOnEpochs }
• Uses rolling average of last 3 epochs' yield amounts and time intervals
• Returns null for all fields if fewer than 2 epochs exist

Testing

• All 414/415 tests pass (1 pre-existing failure in indexer.test.ts trace span logging)
• All yield, webhook, and notification tests pass
• TypeScript compiles cleanly with tsc --noEmit

Migration

• New migration: 030_epoch_closed_at.sql — adds closed_at TIMESTAMPTZ to epochs table

Closes #818
Closes #819
Closes #820
Closes #821

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