feat: VaR/PnL schedulers + snapshots DB + page sur bouton

Backend:
- Tables var_snapshots + pnl_snapshots dans SQLite (contexte macro + prix tickers)
- var_service.py : save_var_snapshot, save_pnl_snapshot + fonctions get_*
- var_scheduler.py : threads APScheduler pour VaR (défaut 6h) et PnL (défaut 1h)
- router var.py : /run-now (POST compute+save), /latest, /snapshots, /pnl/run-now,
  /pnl/latest, /scheduler/status, /scheduler/config
- main.py : démarrage des deux schedulers au startup

Frontend:
- VaRAnalysis.tsx : plus d'auto-fetch ; charge le dernier snapshot DB au mount ;
  bouton "Calculer" → POST /run-now ; erreur backend = message clair ; historique
  de snapshots sélectionnables
- Config.tsx : section "Schedulers VaR & PnL" dans l'onglet cycle avec toggle
  enable/disable, intervalle, et boutons "Snapshot maintenant"

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/services/database.py

@@ -398,6 +398,51 @@ def init_db():
     except Exception:
         pass
 
+    c.execute("""CREATE TABLE IF NOT EXISTS var_snapshots (
+        id INTEGER PRIMARY KEY AUTOINCREMENT,
+        computed_at TEXT NOT NULL,
+        confidence REAL NOT NULL DEFAULT 0.95,
+        horizon_days INTEGER NOT NULL DEFAULT 1,
+        lookback_days INTEGER NOT NULL DEFAULT 252,
+        default_iv REAL NOT NULL DEFAULT 0.20,
+        hist_var_1d_pct REAL,
+        hist_cvar_pct REAL,
+        hist_var_1d_eur REAL,
+        param_var_1d_pct REAL,
+        param_cvar_pct REAL,
+        mc_var_1d_pct REAL,
+        mc_cvar_pct REAL,
+        n_positions INTEGER,
+        total_notional_eur REAL,
+        data_source TEXT,
+        breach_rate_pct REAL,
+        kupiec_ok INTEGER,
+        macro_regime TEXT,
+        ticker_prices TEXT,
+        full_result TEXT
+    )""")
+    try:
+        c.execute("CREATE INDEX IF NOT EXISTS idx_var_snap_ts ON var_snapshots(computed_at DESC)")
+    except Exception:
+        pass
+
+    c.execute("""CREATE TABLE IF NOT EXISTS pnl_snapshots (
+        id INTEGER PRIMARY KEY AUTOINCREMENT,
+        snapped_at TEXT NOT NULL,
+        n_open INTEGER,
+        n_closed INTEGER,
+        total_capital_eur REAL,
+        total_pnl_pct REAL,
+        total_pnl_eur REAL,
+        ticker_prices TEXT,
+        macro_regime TEXT,
+        trades_snapshot TEXT
+    )""")
+    try:
+        c.execute("CREATE INDEX IF NOT EXISTS idx_pnl_snap_ts ON pnl_snapshots(snapped_at DESC)")
+    except Exception:
+        pass
+
     try:
         c.execute("CREATE INDEX IF NOT EXISTS idx_kb_category ON knowledge_base(category, status)")
         c.execute("CREATE INDEX IF NOT EXISTS idx_rs_version ON reasoning_state(version DESC)")