fix(preferences): Remove gpt-4 default and update Remote Providers title

**Problem 1 (Issue 4): Default model shows gpt-4 when no provider configured**
- PreferencesView.swift line 403 had hardcoded fallback: defaultModel = "gpt-4"
- Causes confusion for users without OpenAI API key
- ConversationModel.swift getDefaultModel() already returns empty string

**Problem 2 (Issue 3): Remote Providers tab title shows 'API Endpoints'**
- PreferencesSection enum was renamed to 'Remote Providers'
- But EndpointManagementView.swift line 78 still showed old title

**Solution:**
- Changed default value from "gpt-4" to "" in PreferencesView.swift
- Updated headerSection title from "API Endpoints" to "Remote Providers"
- Now consistent with PreferencesSection enum naming

**Files changed:**
- Sources/UserInterface/PreferencesView.swift line 403: Empty default
- Sources/UserInterface/EndpointManagementView.swift line 78: Title update

**Testing:**
✅ Build: PASS
✅ Code review: Matches existing getDefaultModel() behavior
✅ Consistency: Remote Providers naming unified

Author: fewtarius

Sources/UserInterface/EndpointManagementView.swift

@@ -75,7 +75,7 @@ struct EndpointManagementView: View {
 
     private var headerSection: some View {
         VStack(alignment: .leading, spacing: 8) {
-            Text("API Endpoints")
+            Text("Remote Providers")
                 .font(.title2)
                 .fontWeight(.semibold)
             Text("Configure AI provider endpoints for multi-model support")

Sources/UserInterface/PreferencesView.swift

@@ -400,7 +400,7 @@ struct PreferencesSectionRow: View {
 
 struct GeneralPreferencesView: View {
     @EnvironmentObject private var endpointManager: EndpointManager
-    @AppStorage("defaultModel") private var defaultModel: String = "gpt-4"
+    @AppStorage("defaultModel") private var defaultModel: String = ""
     @State private var availableModels: [String] = []
     @State private var loadingModels: Bool = false
     @AppStorage("userName") private var userName: String = ""