Spike 3: Sub-agent infrastructure fixes for multi-agent coordination

- Fix CLAUDECODE env var blocking nested Claude Code sessions
- Add drain-based event_log for reliable get_agent_output polling
- Add non-SSE get_agent_output fallback (critical for MCP tool calls)
- Preserve worktrees on agent stop instead of destroying work
- Reap zombie processes with child.wait() after kill
- Increase broadcast buffer from 256 to 1024
- Engineer supervisor and coder prompts in project.toml
- Point .mcp.json to test port 3002

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

server/src/config.rs

@@ -11,6 +11,7 @@ pub struct ProjectConfig {
 }
 
 #[derive(Debug, Clone, Deserialize)]
+#[allow(dead_code)]
 pub struct ComponentConfig {
     pub name: String,
     #[serde(default = "default_path")]