feat: git-based agent version reference and unified outdated badge (0.20.0)

SAC reads latest RDP/ssh-monitor versions from configured git repos for outdated detection, update targets, and settings test-git.

backend/app/schemas/list_models.py

@@ -49,6 +49,10 @@ class HostListResponse(BaseModel):
     page: int
     page_size: int
     latest_agent_versions: dict[str, str] = Field(default_factory=dict)
+    reference_agent_versions: dict[str, str] = Field(
+        default_factory=dict,
+        description="Эталон для «устарела»: max(git latest, min, max в fleet)",
+    )
 
 
 class EventSummary(BaseModel):