Build invoice payment timeline reconstructor from event history

[Kingsman-99]

Description

Debugging payment disputes or auditing invoice lifecycles requires a chronologically ordered view of every state change and payment event for an invoice, but these events are scattered across Soroban event streams and Horizon payment records. This issue adds a PaymentTimelineReconstructor that aggregates events from both sources, normalizes them into a unified TimelineEntry format, and returns a sorted, deduplicated timeline for a given invoice.

Technical Context

• New file: src/timeline/PaymentTimelineReconstructor.ts; types: TimelineEntry, TimelineSource, ReconstructedTimeline in src/types/timeline.ts
• TimelineEntry: { timestamp: number; ledger: number; type: TimelineEventType; data: Record<string, unknown>; source: 'soroban'|'horizon' }
• TimelineEventType union: 'invoice_created'|'payment_received'|'status_changed'|'recipient_added'|'recipient_rerouted'|'sla_breached'
• Deduplication uses (ledger, txHash, type) as the composite key to eliminate events that appear in both sources
• reconstructor.rebuild(invoiceId, options?: { from?: number; to?: number; types?: TimelineEventType[] }): Promise<ReconstructedTimeline> is the primary API

Acceptance Criteria

• A timeline for an invoice with 3 Soroban events and 2 Horizon payment records returns 5 deduplicated entries sorted by timestamp ascending
• An event present in both Soroban and Horizon streams appears exactly once in the output (deduplication)
• from / to ledger range filters exclude entries outside the range
• types filter returns only entries whose type is in the provided array
• ReconstructedTimeline includes { totalEvents, sources: { soroban: number; horizon: number }, deduplicatedCount } in its metadata
• All CI checks (npm test, npm run build, ESLint) pass and the branch has no merge conflicts

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