feat: implement Radar backend tRPC procedures with repository extensions

Add five new tRPC query procedures powering the Radar page's per-agent
behavioral metrics (questions asked, subagent spawns, compaction events,
inter-agent messages) plus the batch repository methods they require.

Repository changes:
- LogChunkRepository: add findByAgentIds() for batch fetching without N+1
- ConversationRepository: add countByFromAgentIds() and findByFromAgentId()
- Drizzle adapters: implement all three new methods using inArray()
- InMemoryConversationRepository (integration test): implement new methods

tRPC procedures added:
- agent.listForRadar: filtered agent list with per-agent metrics computed
  from log chunks (questionsCount, subagentsCount, compactionsCount) and
  conversation counts (messagesCount); supports timeRange/status/mode/initiative filters
- agent.getCompactionEvents: compact system init chunks for one agent (cap 200)
- agent.getSubagentSpawns: Agent tool_use entries with prompt preview (cap 200)
- agent.getQuestionsAsked: AskUserQuestion tool calls with questions array (cap 200)
- conversation.getByFromAgent: conversations by fromAgentId with toAgentName resolved

All 13 new unit tests pass; existing test suite unaffected.

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

apps/server/db/repositories/drizzle/log-chunk.ts

@@ -4,7 +4,7 @@
  * Implements LogChunkRepository interface using Drizzle ORM.
  */
 
-import { eq, asc, max } from 'drizzle-orm';
+import { eq, asc, max, inArray } from 'drizzle-orm';
 import { nanoid } from 'nanoid';
 import type { DrizzleDatabase } from '../../index.js';
 import { agentLogChunks } from '../../schema.js';
@@ -41,6 +41,20 @@ export class DrizzleLogChunkRepository implements LogChunkRepository {
       .orderBy(asc(agentLogChunks.createdAt));
   }
 
+  async findByAgentIds(agentIds: string[]): Promise<{ agentId: string; content: string; sessionNumber: number; createdAt: Date }[]> {
+    if (agentIds.length === 0) return [];
+    return this.db
+      .select({
+        agentId: agentLogChunks.agentId,
+        content: agentLogChunks.content,
+        sessionNumber: agentLogChunks.sessionNumber,
+        createdAt: agentLogChunks.createdAt,
+      })
+      .from(agentLogChunks)
+      .where(inArray(agentLogChunks.agentId, agentIds))
+      .orderBy(asc(agentLogChunks.createdAt));
+  }
+
   async deleteByAgentId(agentId: string): Promise<void> {
     await this.db
       .delete(agentLogChunks)