feat(dashboard): streamlit skeleton + Overview page + data layer

Aggiunge scheletro multipage Streamlit per Phase 1:
- modulo data.py con helper (list_runs_df, get_run_overview,
  generations_df, evaluations_df, genomes_df) sopra Repository.
- streamlit_app.py entry point con DB_PATH da env.
- pages/01_overview.py per elenco run + metriche + config JSON.
- smoke test import di multi_swarm.dashboard.data.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/multi_swarm/dashboard/data.py

@@ -0,0 +1,54 @@
+from __future__ import annotations
+
+import json
+from pathlib import Path
+from typing import Any
+
+import pandas as pd  # type: ignore[import-untyped]
+
+from ..persistence.repository import Repository
+
+
+def get_repo(db_path: str | Path) -> Repository:
+    return Repository(db_path=db_path)
+
+
+def list_runs_df(repo: Repository) -> pd.DataFrame:
+    return pd.DataFrame(repo.list_runs())
+
+
+def get_run_overview(repo: Repository, run_id: str) -> dict[str, Any]:
+    run = repo.get_run(run_id)
+    return {
+        "name": run["name"],
+        "started_at": run["started_at"],
+        "completed_at": run["completed_at"],
+        "status": run["status"],
+        "total_cost_usd": run["total_cost_usd"],
+        "config": json.loads(run["config_json"]),
+    }
+
+
+def generations_df(repo: Repository, run_id: str) -> pd.DataFrame:
+    return pd.DataFrame(repo.list_generations(run_id))
+
+
+def evaluations_df(repo: Repository, run_id: str) -> pd.DataFrame:
+    return pd.DataFrame(repo.list_evaluations(run_id))
+
+
+def genomes_df(
+    repo: Repository, run_id: str, generation_idx: int | None = None
+) -> pd.DataFrame:
+    rows = repo.list_genomes(run_id, generation_idx)
+    flat: list[dict[str, Any]] = []
+    for r in rows:
+        payload = json.loads(r["payload_json"])
+        flat.append(
+            {
+                "id": r["id"],
+                "generation_idx": r["generation_idx"],
+                **payload,
+            }
+        )
+    return pd.DataFrame(flat)