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/database.py

@@ -311,6 +311,9 @@ def init_db():
         "auto_cycle_similarity_threshold": "0.30",
         "min_ev_threshold": "0.0",
         "min_score_threshold": "0",
+        "trade_budget_eur": "5000",
+        "preferred_horizon_min": "30",
+        "preferred_horizon_max": "180",
         "exit_defaults": json.dumps({
             "target_pct": 30.0,
             "stop_loss_pct": -50.0,