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/conversation-repository.ts

@@ -20,4 +20,18 @@ export interface ConversationRepository {
   findById(id: string): Promise<Conversation | null>;
   findPendingForAgent(toAgentId: string): Promise<Conversation[]>;
   answer(id: string, answer: string): Promise<Conversation | null>;
+
+  /**
+   * Count conversations grouped by fromAgentId for a batch of agent IDs.
+   * Returns only agents that have at least one conversation (count > 0).
+   * Used by listForRadar to compute messagesCount without N+1 queries.
+   */
+  countByFromAgentIds(agentIds: string[]): Promise<{ agentId: string; count: number }[]>;
+
+  /**
+   * Find all conversations initiated by a given agent, ordered by createdAt ascending.
+   * Used by conversation.getByFromAgent drilldown procedure.
+   * Cap at 200 results.
+   */
+  findByFromAgentId(agentId: string): Promise<Conversation[]>;
 }