feat: Implement Worker Service v2 with improved architecture

- Complete rewrite of the Worker Service following object-oriented principles.
- Introduced a single long-lived database connection to reduce overhead.
- Implemented event-driven queues to eliminate polling.
- Added DRY utilities for pagination and settings management.
- Reduced code size significantly from 1173 lines to approximately 600-700 lines.
- Created various composed services including DatabaseManager, SessionManager, and SDKAgent.
- Enhanced SSE broadcasting capabilities for real-time client updates.
- Established a structured approach for session lifecycle management and event handling.
- Introduced type safety with shared TypeScript interfaces for better maintainability.

src/services/worker/SettingsManager.ts

@@ -0,0 +1,68 @@
+/**
+ * SettingsManager: DRY settings CRUD utility
+ *
+ * Responsibility:
+ * - DRY helper for viewer settings CRUD
+ * - Eliminates duplication in settings read/write logic
+ * - Type-safe settings management
+ */
+
+import { DatabaseManager } from './DatabaseManager.js';
+import { logger } from '../../utils/logger.js';
+import type { ViewerSettings } from '../worker-types.js';
+
+export class SettingsManager {
+  private dbManager: DatabaseManager;
+  private readonly defaultSettings: ViewerSettings = {
+    sidebarOpen: true,
+    selectedProject: null,
+    theme: 'system'
+  };
+
+  constructor(dbManager: DatabaseManager) {
+    this.dbManager = dbManager;
+  }
+
+  /**
+   * Get current viewer settings (with defaults)
+   */
+  getSettings(): ViewerSettings {
+    const db = this.dbManager.getSessionStore().db;
+
+    try {
+      const stmt = db.prepare('SELECT key, value FROM viewer_settings');
+      const rows = stmt.all() as Array<{ key: string; value: string }>;
+
+      const settings: ViewerSettings = { ...this.defaultSettings };
+      for (const row of rows) {
+        const key = row.key as keyof ViewerSettings;
+        if (key in settings) {
+          (settings as any)[key] = JSON.parse(row.value);
+        }
+      }
+
+      return settings;
+    } catch (error) {
+      logger.debug('WORKER', 'Failed to load settings, using defaults', {}, error as Error);
+      return { ...this.defaultSettings };
+    }
+  }
+
+  /**
+   * Update viewer settings (partial update)
+   */
+  updateSettings(updates: Partial<ViewerSettings>): ViewerSettings {
+    const db = this.dbManager.getSessionStore().db;
+
+    const stmt = db.prepare(`
+      INSERT OR REPLACE INTO viewer_settings (key, value)
+      VALUES (?, ?)
+    `);
+
+    for (const [key, value] of Object.entries(updates)) {
+      stmt.run(key, JSON.stringify(value));
+    }
+
+    return this.getSettings();
+  }
+}