Refactor remaining model interfaces to use generated types

[nickna]

Overview

Part of #658 - Refactor all remaining model interfaces to use generated types as source of truth.

Scope

Refactor the remaining model files:

• models/system.ts (28 interfaces)
• models/settings.ts (14 interfaces)
• models/modelCost.ts (13 interfaces)
• models/modelMapping.ts (12 interfaces)
• models/databaseBackup.ts (12 interfaces)
• models/signalr.ts (11 interfaces)
• models/audioConfiguration.ts (14 interfaces)
• models/notifications.ts (3 interfaces)
• models/metadata.ts (10 interfaces)
• models/common-types.ts (14 interfaces)
• And any other remaining files

Total: ~131+ interfaces

Dependencies

• Should be done after core refactorings are complete and proven

Implementation Strategy

Since this is a large group of miscellaneous interfaces, organize by functional area:

Group 1: System & Infrastructure

• system.ts
• databaseBackup.ts
• signalr.ts

Group 2: Configuration & Settings

• settings.ts
• audioConfiguration.ts
• metadata.ts

Group 3: Business Logic

• modelCost.ts
• modelMapping.ts
• notifications.ts

Group 4: Common/Shared

• common-types.ts
• Any remaining files

Implementation Steps

1. Complete inventory of remaining interfaces
2. Group by functional area for easier review
3. Convert each group:
   • System & Infrastructure types
   • Configuration & Settings types
   • Business Logic types
   • Common/Shared types
4. Update all service imports
5. Run comprehensive type validation
6. Full SDK and WebUI build test

Special Considerations

• common-types.ts may have types used across many files
• Some types might be purely client-side constructs
• Watch for circular dependencies

Validation

• All remaining interfaces converted
• Type validation suite passes
• SDK builds without warnings
• WebUI builds and runs correctly
• No TypeScript errors in IDE

Definition of Done

• All model files use generated types
• No manual interface duplication remains
• All tests pass
• Documentation updated
• PR reviewed and merged