perf(agent): stabilkan async & parallel — satu runtime, bounded concurrency, isolasi error

Seperti Claude Code: satu runtime shared, concurrency dibatasi, error
subagent terisolasi (satu node gagal tidak menggagalkan cycle).

- feat(runtime): global tokio runtime via OnceLock — ganti 9+ titik
  Runtime::new() per tool call (spawn, parallel_delegate, workflow,
  explore, dir_cache, daemon handler). Hemat resource, hilangkan panic
  path Runtime::new().expect() di daemon compaction.
- fix(workflow): execute_cycle ganti try_join_all (fail-fast) →
  buffer_unordered(8) + isolasi error per node; node gagal di-log dan
  diganti [ERROR], hasil node lain tetap dipakai (Claude Code-style).
- fix(parallel_delegate): spawn subagent dibatasi per batch max_parallel
  (tidak unbounded threads).
- perf(subagent): run_agent adaptif max_tokens (800/1600/4096), temp 0.2,
  truncate tool output 12k, error-recovery note utk tool error berulang.
- test: runtime singleton + block_on (2 test).

apps/infrastructure/src/best_practice/explore.rs

@@ -15,7 +15,7 @@
 //!    read of up to 3 relevant files).
 //! 4. Join the result and return a concise bullet summary as a tool message.
 
-use anyhow::{Context, Result};
+use anyhow::Result;
 use serde_json::{json, Value};
 use tracing::{info, warn};
 
@@ -118,7 +118,7 @@ impl Tool for ExploreCodebase {
             model,
         );
 
-        let rt = tokio::runtime::Runtime::new().context("create explore tokio runtime")?;
+        let rt = crate::runtime::runtime();
         let result = rt.block_on(run_agent(
             subagent_ctx,
             &directive,