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/PaginationHelper.ts

@@ -0,0 +1,92 @@
+/**
+ * PaginationHelper: DRY pagination utility
+ *
+ * Responsibility:
+ * - DRY helper for paginated queries
+ * - Eliminates copy-paste across observations/summaries/prompts endpoints
+ * - Efficient LIMIT+1 trick to avoid COUNT(*) query
+ */
+
+import { DatabaseManager } from './DatabaseManager.js';
+import type { PaginatedResult, Observation, Summary, UserPrompt } from '../worker-types.js';
+
+export class PaginationHelper {
+  private dbManager: DatabaseManager;
+
+  constructor(dbManager: DatabaseManager) {
+    this.dbManager = dbManager;
+  }
+
+  /**
+   * Get paginated observations
+   */
+  getObservations(offset: number, limit: number, project?: string): PaginatedResult<Observation> {
+    return this.paginate<Observation>(
+      'observations',
+      'id, session_db_id, claude_session_id, project, type, title, subtitle, text, concepts, files, prompt_number, created_at, created_at_epoch',
+      offset,
+      limit,
+      project
+    );
+  }
+
+  /**
+   * Get paginated summaries
+   */
+  getSummaries(offset: number, limit: number, project?: string): PaginatedResult<Summary> {
+    return this.paginate<Summary>(
+      'summaries',
+      'id, session_db_id, claude_session_id, project, request, completion, summary, learnings, notes, created_at, created_at_epoch',
+      offset,
+      limit,
+      project
+    );
+  }
+
+  /**
+   * Get paginated user prompts
+   */
+  getPrompts(offset: number, limit: number, project?: string): PaginatedResult<UserPrompt> {
+    return this.paginate<UserPrompt>(
+      'user_prompts',
+      'id, session_db_id, claude_session_id, project, prompt, created_at, created_at_epoch',
+      offset,
+      limit,
+      project
+    );
+  }
+
+  /**
+   * Generic pagination implementation (DRY)
+   */
+  private paginate<T>(
+    table: string,
+    columns: string,
+    offset: number,
+    limit: number,
+    project?: string
+  ): PaginatedResult<T> {
+    const db = this.dbManager.getSessionStore().db;
+
+    let query = `SELECT ${columns} FROM ${table}`;
+    const params: any[] = [];
+
+    if (project) {
+      query += ' WHERE project = ?';
+      params.push(project);
+    }
+
+    query += ' ORDER BY created_at_epoch DESC LIMIT ? OFFSET ?';
+    params.push(limit + 1, offset); // Fetch one extra to check hasMore
+
+    const stmt = db.prepare(query);
+    const results = stmt.all(...params) as T[];
+
+    return {
+      items: results.slice(0, limit),
+      hasMore: results.length > limit,
+      offset,
+      limit
+    };
+  }
+}