SvelteKit-based WebUI (#14839)

.windsurf/rules/sveltekit-architecture.md

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+---
+trigger: manual
+---
+
+# Coding rules
+
+## Svelte & SvelteKit
+
+### Services vs Stores Separation Pattern
+
+#### `lib/services/` - Pure Business Logic
+
+-   **Purpose**: Stateless business logic and external communication
+-   **Contains**:
+    -   API calls to external services (ApiService)
+    -   Pure business logic functions (ChatService, etc.)
+-   **Rules**:
+    -   NO Svelte runes ($state, $derived, $effect)
+    -   NO reactive state management
+    -   Pure functions and classes only
+    -   Can import types but not stores
+    -   Focus on "how" - implementation details
+
+#### `lib/stores/` - Reactive State Management
+
+-   **Purpose**: Svelte-specific reactive state with runes
+-   **Contains**:
+    -   Reactive state classes with $state, $derived, $effect
+    -   Database operations (DatabaseStore)
+    -   UI-focused state management
+    -   Store orchestration logic
+-   **Rules**:
+    -   USE Svelte runes for reactivity
+    -   Import and use services for business logic
+    -   NO direct database operations
+    -   NO direct API calls (use services)
+    -   Focus on "what" - reactive state for UI
+
+#### Enforcement
+
+-   Services should be testable without Svelte
+-   Stores should leverage Svelte's reactivity system
+-   Clear separation: services handle data, stores handle state
+-   Services can be reused across multiple stores
+
+#### Misc
+
+-   Always use `let` for $derived state variables