feat: enrich listWaitingAgents with task/phase/initiative context via DB joins

Replaces the in-memory filter (agentManager.list() + filter) with a direct
repository query that LEFT JOINs tasks, phases, and initiatives to return
taskName, phaseName, initiativeName, and taskDescription alongside agent fields.

- Adds AgentWithContext interface and findWaitingWithContext() to AgentRepository port
- Implements findWaitingWithContext() in DrizzleAgentRepository using getTableColumns
- Wires agentRepository into TRPCContext, CreateContextOptions, and TrpcAdapterOptions
- Adds requireAgentRepository() helper following existing pattern
- Updates listWaitingAgents to use repository query instead of agentManager
- Adds 5 unit tests for findWaitingWithContext() covering all FK join edge cases
- Updates existing AgentRepository mocks to satisfy updated interface

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/server/db/repositories/agent-repository.ts

@@ -8,6 +8,14 @@
 import type { Agent } from '../schema.js';
 import type { AgentMode } from '../../agent/types.js';
 
+/** Agent row enriched with joined task/phase/initiative context fields. */
+export interface AgentWithContext extends Agent {
+  taskName: string | null;
+  phaseName: string | null;
+  initiativeName: string | null;
+  taskDescription: string | null;
+}
+
 /**
  * Agent status values.
  */
@@ -117,4 +125,10 @@ export interface AgentRepository {
    * Throws if agent not found.
    */
   delete(id: string): Promise<void>;
+
+  /**
+   * Find all agents with status 'waiting_for_input', enriched with
+   * task, phase, and initiative names via LEFT JOINs.
+   */
+  findWaitingWithContext(): Promise<AgentWithContext[]>;
 }