fix: 3 個飛輪沉默未打通節點 — 統帥截圖盤出

統帥截圖證據 (Telegram MEDIUM 告警仍走人工審核):
INC-20260411-A03B2E / A2BB29 顯示「[規則匹配]」+ action=unknown-service

節點 1: AutoApprovePolicy 擋下規則匹配 (飛輪主因)
  - ADR-073 規則匹配 confidence=0.0 (防偽造)
  - AutoApprovePolicy.min_confidence=0.50 → 擋下
  - 結果: MEDIUM 規則匹配永遠人工審核，飛輪不轉
  修復: auto_approve.py 加 _is_rule_based 判斷
        (is_rule_based / source=expert_system / rule_id / matched_rule)
        → bypass min_confidence 檢查
        → 驗證: should_auto_approve=True ✅

節點 2: _is_bad_target 漏 unknown-service magic string
  - _resolve_target_from_k8s fallback 產 unknown-service / unknown-pod
  - GAP-A4 Phase 1/2 只擋 'unknown' 而非前綴
  修復: alert_rule_engine.py 加 unknown-/none-/null-/undefined- 前綴黑名單
        → 驗證: 4 個 magic 全 bad ✅

節點 3: stale_ready_tokens_resend 無時效過濾
  - 截圖是 2026-04-11 (4 天前) 告警
  - 舊 labels 過期，重 process 也產不出新 target
  - 壓爆 Ollama + 污染 Telegram 卡片
  修復: decision_manager.py 跳過 > 3 天的 stale incident
        → skip + log stale_ready_token_skipped_too_old

回歸: 113/113

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

apps/api/src/services/alert_rule_engine.py

@@ -143,6 +143,12 @@ def _is_bad_target(target: str, alertname: str) -> bool:
     """
     if not target or target in ("unknown", "none", "null", ""):
         return True
+    # 2026-04-15 Claude Sonnet 4.6 (GAP-A4 Phase 3): 擴充 fallback magic string
+    # 截圖實證：Telegram 卡顯示 target=unknown-service 通過 _is_bad_target
+    # _resolve_target_from_k8s fallback 也會產 unknown-pod/unknown-container
+    _BAD_MAGIC_PREFIXES = ("unknown-", "none-", "null-", "undefined-")
+    if any(target.startswith(p) for p in _BAD_MAGIC_PREFIXES):
+        return True
     if target == alertname:
         return True
     if any(c in target for c in (" ", ":", "(", ")", '"', "'", "<", ">", "{", "}")):