feat: add ownership-costs feature capsule (refs #15)

- Create ownership_costs table for recurring vehicle costs
- Add backend feature capsule with types, repository, service, routes
- Update TCO calculation to use ownership_costs (with fallback to legacy vehicle fields)
- Add taxCosts and otherCosts to TCO response
- Create frontend ownership-costs feature with form, list, API, hooks
- Update TCODisplay to show all cost types

This implements a more flexible approach to tracking recurring ownership costs
(insurance, registration, tax, other) with explicit date ranges and optional
document association.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/features/ownership-costs/index.ts

@@ -0,0 +1,22 @@
+/**
+ * @ai-summary Public API for ownership-costs feature capsule
+ */
+
+// Export service for use by other features
+export { OwnershipCostsService } from './domain/ownership-costs.service';
+
+// Export types
+export type {
+  OwnershipCost,
+  CreateOwnershipCostRequest,
+  UpdateOwnershipCostRequest,
+  OwnershipCostResponse,
+  OwnershipCostStats,
+  OwnershipCostType,
+  CostInterval
+} from './domain/ownership-costs.types';
+
+export { PAYMENTS_PER_YEAR } from './domain/ownership-costs.types';
+
+// Internal: Register routes with Fastify app
+export { ownershipCostsRoutes, registerOwnershipCostsRoutes } from './api/ownership-costs.routes';