chore: opencode冗余清理 + LLM任务级模型选择 + systemd服务化

- 删除 opencode_search.py / mcp_search_server.py 及所有 MCP 引用
- 移除搜索缓存定时任务（scheduled_refresh_search_cache）
- 清理前后端所有 opencode/MCP 代码和注释
- LLM 提供商量换：opencode-go→nvidia(默认)+sensenova(合规审查)
- llm_configs 新增 is_default 字段，API 层互斥逻辑
- 所有定时任务支持独立 LLM 模型选择（LLM_TASK_PROVIDER env）
- compliance_optimizer.py 修复：import os / 解硬编码 / 关键词过滤
- Scheduler 日志修复：始终 INSERT，避免僵尸 running 行
- Systemd 服务化：Restart=always / 单 worker / Type=exec
- 搜索提供商：替换 opencode→360/搜狗/微信（免 Key）
- 更新 AGENTS.md / PROGRESS.md

scripts/search_utils.py

@@ -179,32 +179,6 @@ def _call_bing(api_key: str, api_url: str, query: str, max_results: int) -> List
     } for r in items[:max_results]]
 
 
-def _call_mcp(api_key: str, api_url: str, query: str, max_results: int) -> List[Dict]:
-    """Call the MCP search server directly (no API key needed)."""
-    import subprocess
-    try:
-        r = subprocess.run(
-            [sys.executable, str(PROJECT_ROOT / "scripts" / "mcp_search_server.py"),
-             "--query", query],
-            capture_output=True, text=True, timeout=90,
-        )
-        if r.returncode != 0:
-            logger.warning("MCP搜索子进程返回非零: %s", r.stderr[:100])
-            return []
-        results = json.loads(r.stdout)
-        if isinstance(results, list):
-            for res in results:
-                res["source"] = "opencode"
-            return results[:max_results]
-    except json.JSONDecodeError as e:
-        logger.warning("MCP搜索JSON解析失败: %s", e)
-    except subprocess.TimeoutExpired:
-        logger.warning("MCP搜索超时 (90s)")
-    except Exception as e:
-        logger.warning("MCP搜索失败: %s", e)
-    return []
-
-
 def _call_360(api_key: str, api_url: str, query: str, max_results: int) -> List[Dict]:
     """360搜索（HTML爬取，无需 API Key）"""
     from bs4 import BeautifulSoup
@@ -311,7 +285,6 @@ _PROVIDER_CALLS = {
     "qiniu": _call_qiniu,
     "tinyfish": _call_tinyfish,
     "bing": _call_bing,
-    "mcp": _call_mcp,
     "360": _call_360,
     "sogou": _call_sogou,
     "wechat": _call_wechat,
@@ -325,7 +298,7 @@ def search(query: str, max_results: int = 5) -> List[Dict]:
         if (p.get("usage_today") or 0) >= (p.get("daily_limit") or 99999):
             logger.info("提供商 %s 已达日限 %s，跳过", p.get("name"), p.get("daily_limit"))
             continue
-        no_key_types = {"mcp", "360", "sogou", "wechat"}
+        no_key_types = {"360", "sogou", "wechat"}
         if not p.get("api_key") and p.get("provider_type") not in no_key_types:
             logger.info("提供商 %s 未配置 API Key，跳过", p.get("name"))
             continue