fix(alert-format): 移除 [LLM_OPENCLAW_NEMO] prefix + 擴大根因/建議字數

- root_cause: 移除 [source.upper()] 前綴，直接顯示 AI 分析文字
- root_cause 截斷: 80→150 字
- suggested_action 截斷: 50→80 字
- AI provider 來源已在訊息標頭 「🤖 OpenClaw Nemo 仲裁」顯示，不需在根因重複

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

apps/api/src/services/decision_manager.py

@@ -125,8 +125,8 @@ async def _push_decision_to_telegram(
             approval_id=approval_id,
             risk_level=risk_level,
             resource_name=target[:50],
-            root_cause=f"[{source.upper()}] {reasoning[:80]}" if reasoning else description[:100],
-            suggested_action=action[:50] if action else "待分析",
+            root_cause=reasoning[:150] if reasoning else description[:150],  # 2026-04-03 ogt: 移除 [LLM_xxx] prefix，擴大至 150 字
+            suggested_action=action[:80] if action else "待分析",  # 2026-04-03 ogt: 50→80 字
             estimated_downtime="5-15 min",
             primary_responsibility="INFRA",
             confidence=confidence,