fix: handle both string[] and object[] formats in provider-models cache

Category delegation fails when provider-models.json contains model objects
with metadata (id, provider, context, output) instead of plain strings.
Line 196 in model-availability.ts assumes string[] format, causing:
  - Object concatenation: `${providerId}/${modelId}` becomes "ollama/[object Object]"
  - Empty availableModels Set passed to resolveModelPipeline()
  - Error: "Model not configured for category"

This is the root cause of issue #1508 where delegate_task(category='quick')
fails despite direct agent routing (delegate_task(subagent_type='explore'))
working correctly.

Changes:
- model-availability.ts: Add type check to handle both string and object formats
- connected-providers-cache.ts: Update ProviderModelsCache interface to accept both formats
- model-availability.test.ts: Add 4 test cases for object[] format handling

Direct agent routing bypasses fetchAvailableModels() entirely, explaining why
it works while category routing fails. This fix enables category delegation
to work with manually-populated Ollama model caches.

Fixes #1508

src/shared/connected-providers-cache.ts

@@ -11,8 +11,16 @@ interface ConnectedProvidersCache {
 	updatedAt: string
 }
 
+interface ModelMetadata {
+	id: string
+	provider?: string
+	context?: number
+	output?: number
+	name?: string
+}
+
 interface ProviderModelsCache {
-	models: Record<string, string[]>
+	models: Record<string, string[] | ModelMetadata[]>
 	connected: string[]
 	updatedAt: string
 }