fix: 审计修复 — diagnose/file-diff 端点静默吞错改为 logger.debug/warning

B1: diagnose 磁盘和路径检查 except:pass 改为 logger.debug()
B2: file-diff SSH失败无日志改为 logger.warning()

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

server/api/sync_v2.py

@@ -538,10 +538,8 @@ async def diagnose_push(
                     result["disk_used_pct"] = int(parts[4].replace("%", ""))  # e.g. 72
                 except ValueError:
                     pass
-    except Exception:
-        pass
-
-    # 3. Target path existence + permissions
+    except Exception as e:
+        logger.debug(f"Diagnose disk check failed for server {payload.server_id}: {e}")
     try:
         r = await exec_ssh_command(server, f"ls -ld {safe_dest} 2>&1", timeout=10)
         if r["exit_code"] == 0:
@@ -552,8 +550,8 @@ async def diagnose_push(
         else:
             result["path_exists"] = False
             result["errors"].append(f"目标路径不存在: {dest}")
-    except Exception:
-        pass
+    except Exception as e:
+        logger.debug(f"Diagnose path check failed for server {payload.server_id}: {e}")
 
     # 4. Write test
     if result["path_exists"]:
@@ -675,8 +673,9 @@ async def file_diff(
         else:
             # File doesn't exist on remote — treat as empty (all local lines are additions)
             remote_exists = False
-    except Exception:
+    except Exception as e:
         # SSH failed — report error
+        logger.warning(f"File diff remote read failed for server {payload.server_id}: {e}")
         remote_exists = None
 
     # Compute unified diff