feat(dashboard): scaffolding Streamlit con cliente HTTP y health check

CoreClient (httpx sync, 2 retries) cubre todos los endpoints del core y mapea
404/409/422 a {"error": ...}. app.py monta la página raíz con sidebar de branding
y un health-check del core.

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

dashboard/src/agentforge_dashboard/client.py

@@ -0,0 +1,71 @@
+"""Cliente HTTP tipado al core. Encapsula httpx y mapea respuestas a dicts."""
+
+from __future__ import annotations
+
+import os
+from typing import Any
+
+import httpx
+
+
+class CoreClient:
+    """Cliente sincrono (Streamlit es sync). 2 retries con httpx Transport."""
+
+    def __init__(self, base_url: str | None = None, timeout: float = 30.0) -> None:
+        self.base_url = base_url or os.getenv("AGENTFORGE_CORE_URL", "http://localhost:8000")
+        transport = httpx.HTTPTransport(retries=2)
+        self._client = httpx.Client(base_url=self.base_url, timeout=timeout, transport=transport)
+
+    def health(self) -> dict:
+        return self._get("/health")
+
+    def list_agents(self) -> list[dict]:
+        return self._get("/agents")
+
+    def get_agent(self, name: str) -> dict:
+        return self._get(f"/agents/{name}")
+
+    def list_versions(self, name: str) -> list[dict]:
+        return self._get(f"/agents/{name}/versions")
+
+    def diff_versions(self, name: str, v_from: str, v_to: str) -> dict:
+        return self._get(f"/agents/{name}/versions/{v_from}/diff/{v_to}")
+
+    def invoke_agent(self, name: str, body: dict) -> dict:
+        return self._post(f"/agents/{name}/invoke", body)
+
+    def get_execution(self, trace_id: str) -> dict:
+        return self._get(f"/executions/{trace_id}")
+
+    def list_executions(self) -> list[dict]:
+        return self._get("/executions")
+
+    def approve(self, trace_id: str, body: dict) -> dict:
+        return self._post(f"/executions/{trace_id}/approve", body)
+
+    def reject(self, trace_id: str, body: dict) -> dict:
+        return self._post(f"/executions/{trace_id}/reject", body)
+
+    def list_violations(self, **filters: Any) -> list[dict]:
+        params = {k: v for k, v in filters.items() if v is not None}
+        return self._get("/violations", params=params)
+
+    def list_policies(self) -> list[dict]:
+        return self._get("/policies")
+
+    def list_policy_versions(self, name: str) -> list[dict]:
+        return self._get(f"/policies/{name}/versions")
+
+    # ----- helpers privados -----
+
+    def _get(self, path: str, params: dict | None = None) -> Any:
+        r = self._client.get(path, params=params)
+        r.raise_for_status()
+        return r.json()
+
+    def _post(self, path: str, body: dict) -> Any:
+        r = self._client.post(path, json=body)
+        if r.status_code in {404, 409, 422}:
+            return {"error": r.json()}
+        r.raise_for_status()
+        return r.json()