feat: trade mandate (budget + horizon) wired end-to-end

- database.py: add trade_budget_eur / preferred_horizon_min/max config
  defaults and include them in cycle config migrations
- auto_cycle.py: read trade params from config and inject into cycle_meta
- ai_analyzer.py: inject INVESTOR TRADE MANDATE block into scoring and
  suggestion prompts so GPT-4o penalises horizon mismatches and sizes
  within the capital cap
- Config.tsx: Trade Parameters card with budget + horizon sliders and live
  mandate summary
- TradeIdeas.tsx: horizon filter pills (< 1M / 1-3M / 3-6M / > 6M) and
  budget/horizon indicator pulled from saved config
- useApi.ts: extend useUpdateCycleConfig type with new config fields

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

backend/services/auto_cycle.py

@@ -255,6 +255,10 @@ def run_cycle_once(trigger: str = "auto") -> Dict[str, Any]:
             _market_session = "after_hours"
             _market_note = "After-hours US — prix indicatifs, liquidité réduite."
 
+        _budget_eur       = float(get_config("trade_budget_eur") or "5000")
+        _horizon_min      = int(get_config("preferred_horizon_min") or "30")
+        _horizon_max      = int(get_config("preferred_horizon_max") or "180")
+
         cycle_meta = {
             "current_cycle_ts": _now.isoformat(),
             "last_cycle_ts": _last_cycle_ts_str,
@@ -265,6 +269,9 @@ def run_cycle_once(trigger: str = "auto") -> Dict[str, Any]:
             "is_weekend": _is_weekend,
             "market_session": _market_session,
             "market_note": _market_note,
+            "trade_budget_eur": _budget_eur,
+            "preferred_horizon_min": _horizon_min,
+            "preferred_horizon_max": _horizon_max,
         }
         logger.info(
             f"[Cycle {run_id[:16]}] Cycle meta: delta={_delta_minutes:.0f}min depuis dernier cycle"