feat: paper trading capital controls — add, withdraw, and full reset

Three distinct capital operations on the Trading Controls page:

- Set Capital: overwrites pool balances to a new amount (existing)
- Add/Withdraw: adjusts active pool by a delta without touching
  positions, orders, or history. Validates sufficient balance for
  withdrawals. Logged to reserve_pool_ledger as manual_adjustment.
- Reset Everything: nuclear option — deletes all positions, orders,
  trading decisions, stop levels, snapshots, backtests, notifications,
  and circuit breaker events, then resets capital fresh. Red button
  with double-confirmation dialog.

Backend: POST /api/trading/capital/adjust and POST /api/trading/reset
Frontend: CapitalCard rebuilt with three sections and confirmation UIs

services/trading/app.py

@@ -354,6 +354,119 @@ async def set_capital(body: CapitalRequest) -> dict[str, Any]:
     }
 
 
+@app.post("/api/trading/capital/adjust")
+async def adjust_capital(body: dict[str, Any]) -> dict[str, Any]:
+    """Add or subtract capital from the active pool without resetting anything.
+
+    Body: { "amount": 5000 } to add, { "amount": -2000 } to subtract.
+    Positions, orders, decisions, and history are untouched.
+    """
+    if engine is None:
+        raise HTTPException(503, "Engine not initialised")
+
+    amount = body.get("amount", 0)
+    if not isinstance(amount, (int, float)) or amount == 0:
+        raise HTTPException(400, "amount must be a non-zero number")
+
+    ps = engine.portfolio_state
+    if ps is None:
+        raise HTTPException(400, "No portfolio state — set capital first")
+
+    new_active = ps.active_pool + amount
+    if new_active < 0:
+        raise HTTPException(400, f"Cannot subtract ${abs(amount):,.2f} — only ${ps.active_pool:,.2f} available in active pool")
+
+    previous_active = ps.active_pool
+    ps.active_pool = new_active
+    ps.cash = ps.cash + amount
+    ps.total_value = ps.total_value + amount
+
+    # Record in reserve pool ledger for audit
+    if engine.pool:
+        try:
+            trigger = "manual_adjustment"
+            note = f"{'Added' if amount > 0 else 'Withdrew'} ${abs(amount):,.2f} (active pool: ${previous_active:,.2f} → ${new_active:,.2f})"
+            await engine.pool.execute(
+                "INSERT INTO reserve_pool_ledger (amount, balance_after, trigger_type, notes) "
+                "VALUES ($1, $2, $3, $4)",
+                amount, new_active, trigger, note,
+            )
+        except Exception:
+            pass
+
+    return {
+        "adjusted": amount,
+        "active_pool": ps.active_pool,
+        "reserve_pool": ps.reserve_pool,
+        "total_value": ps.total_value,
+    }
+
+
+@app.post("/api/trading/reset")
+async def reset_paper_trading(body: CapitalRequest) -> dict[str, Any]:
+    """Full paper trading reset: clear all positions, orders, decisions,
+    stop levels, and snapshots, then reset capital to the specified amount.
+
+    This is a destructive operation — all trading history is wiped.
+    """
+    if engine is None:
+        raise HTTPException(503, "Engine not initialised")
+
+    capital = body.initial_capital
+    if capital <= 0:
+        raise HTTPException(400, "initial_capital must be positive")
+
+    reserve_pct = engine.config.reserve_siphon_pct
+    reserve = capital * reserve_pct
+    active = capital - reserve
+
+    # Clear trading state in the database
+    if engine.pool:
+        try:
+            async with engine.pool.acquire() as conn:
+                async with conn.transaction():
+                    # Order matters due to FK constraints
+                    await conn.execute("DELETE FROM backtest_trades")
+                    await conn.execute("DELETE FROM backtest_runs")
+                    await conn.execute("DELETE FROM position_stop_levels")
+                    await conn.execute("DELETE FROM trading_decisions")
+                    await conn.execute("DELETE FROM portfolio_snapshots")
+                    await conn.execute("DELETE FROM reserve_pool_ledger")
+                    await conn.execute("DELETE FROM risk_tier_history")
+                    await conn.execute("DELETE FROM circuit_breaker_events")
+                    await conn.execute("DELETE FROM notifications")
+                    # Clear orders and their events
+                    await conn.execute("DELETE FROM order_events")
+                    await conn.execute("DELETE FROM orders")
+                    # Re-seed reserve pool ledger
+                    await conn.execute(
+                        "INSERT INTO reserve_pool_ledger (amount, balance_after, trigger_type, notes) "
+                        "VALUES ($1, $2, 'initial', $3)",
+                        reserve, reserve,
+                        f"Paper trading reset to ${capital:,.2f}",
+                    )
+        except Exception:
+            logger.exception("Failed to clear trading tables during reset")
+            raise HTTPException(500, "Database reset failed")
+
+    # Reset in-memory engine state
+    from services.trading.models import CircuitBreakerState, PortfolioState
+    engine.portfolio_state = PortfolioState(
+        total_value=capital,
+        cash=capital,
+        active_pool=active,
+        reserve_pool=reserve,
+    )
+    engine.circuit_breaker_state = CircuitBreakerState()
+
+    return {
+        "reset": True,
+        "initial_capital": capital,
+        "active_pool": active,
+        "reserve_pool": reserve,
+    }
+
+
 # ---------------------------------------------------------------------------
 # Decision Audit Trail
 # ---------------------------------------------------------------------------