feat(automerge): implement Phase 3 - History Feature UI

[Masked-Kunsiquat]

Add comprehensive history timeline UI for viewing all changes to a trip. Follows three-layer architecture (engine → hooks → UI) as specified in AUTOMERGE_IMPLEMENTATION_PLAN.md.

Engine Layer (Pure Functions):

• history-parser.ts: Parse Automerge.getHistory() into structured changes
• format-changes.ts: Transform parsed changes into human-readable UI text

Hooks Layer (React Integration):

• use-trip-history.ts: Load Automerge doc and parse operation log
• use-formatted-history.ts: Combine history + participants for formatted output

UI Layer (Components):

• HistoryTimeline.tsx: FlatList timeline of all changes (newest-first)
• ChangeDetailCard.tsx: Expandable card with field-level change details
• TripHistoryScreen.tsx: Full screen history view with loading/error states

Integration:

• Added History card to Trip Dashboard (TripActionCards)
• Created route: /trips/[id]/history
• Supports all change types: trip metadata, participants, expenses, settlements
• Human-readable descriptions (e.g., "Alice paid $50.00", "Updated trip name")
• Relative timestamps (e.g., "2 hours ago", "3 days ago")
• Field-by-field diffs in expandable cards
• Empty state handling for trips without Automerge docs

Testing:

• All files pass TypeScript type-check
• All files pass ESLint validation
• Uses deterministic error handling (createAppError)
• Follows accessibility guidelines (screen reader labels, touch targets)

Implements Phase 3 tasks from AUTOMERGE_IMPLEMENTATION_PLAN.md.

🤖 Generated with Claude Code

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