Refactor: export useSlmApi internal interfaces to shared types

[mrveiss]

Context

Discovered during implementation of #3167 (PR #3180). When replacing any types, consumers had to duplicate interface definitions instead of importing them.

Problem

useSlmApi.ts defines 57 interfaces inside the composable function scope. None are exported. This forces consumers to:

• Use any/unknown (what Enhancement: replace remaining ~167 any types in Vue components and low-count TS files #3167 was fixing)
• Duplicate interfaces locally (what PR fix(frontend): replace remaining any types in Vue/TS files (#3167) #3180 did for MonitoringError in AdminMonitoringView.vue)
• Use ReturnType tricks (what PR fix(frontend): replace remaining any types in Vue/TS files (#3167) #3180 did for LoginView.vue)

Example: AdminMonitoringView.vue had to define its own MonitoringError interface matching the shape of items in RecentErrorsResponse.errors, because RecentError is scoped inside useSlmApi().

Affected Interfaces (sample)

• RecentError, RecentErrorsResponse — used by monitoring views
• FleetCert — used by security/certificate views
• SystemHealth, ErrorStats, MetricSummary — used by admin monitoring
• All 10 security response types (see Enhancement: add typed response interfaces for security API endpoints #3184)

Solution

Move shared response interfaces to src/types/slm.ts (or a new src/types/api-responses.ts) and import them in both useSlmApi.ts and consumer components. This eliminates duplication and makes type-safe API consumption straightforward.

Discovered During

Implementation of #3167 (PR #3180)