feat: Add position scaling for strong confirmation signals

**Feature: Position Scaling**
Allows adding to existing profitable positions when high-quality signals confirm trend strength.

**Configuration (config/trading.ts):**
- enablePositionScaling: false (disabled by default - enable after testing)
- minScaleQualityScore: 75 (higher bar than initial 60)
- minProfitForScale: 0.4% (must be at/past TP1)
- maxScaleMultiplier: 2.0 (max 200% of original size)
- scaleSizePercent: 50% (add 50% of original position)
- minAdxIncrease: 5 (ADX must strengthen)
- maxPricePositionForScale: 70% (don't chase resistance)

**Validation Logic (check-risk endpoint):**
Same-direction signal triggers scaling check if enabled:
1. Quality score ≥75 (stronger than initial entry)
2. Position profitable ≥0.4% (at/past TP1)
3. ADX increased ≥5 points (trend strengthening)
4. Price position <70% (not near resistance)
5. Total size <2x original (risk management)
6. Returns 'allowed: true, reason: Position scaling' if all pass

**Execution (execute endpoint):**
- Opens additional position at scale size (50% of original)
- Updates ActiveTrade: timesScaled, totalScaleAdded, currentSize
- Tracks originalAdx from first entry for comparison
- Returns 'action: scaled' with scale details

**ActiveTrade Interface:**
Added fields:
- originalAdx?: number (for scaling validation)
- timesScaled?: number (track scaling count)
- totalScaleAdded?: number (total USD added)

**Example Scenario:**
1. LONG SOL at $176 (quality: 45, ADX: 13.4) - weak but entered
2. Price hits $176.70 (+0.4%) - at TP1
3. New LONG signal (quality: 78, ADX: 19) - strong confirmation
4. Scaling validation: ✅ Quality 78 ✅ Profit +0.4% ✅ ADX +5.6 ✅ Price 68%
5. Adds 50% more position at $176.70
6. Total position: 150% of original size

**Conservative Design:**
- Disabled by default (requires manual enabling)
- Only scales INTO profitable positions (never averaging down)
- Requires significant quality improvement (75 vs 60)
- Requires trend confirmation (ADX increase)
- Hard cap at 2x original size
- Won't chase near resistance levels

**Next Steps:**
1. Enable in settings: ENABLE_POSITION_SCALING=true
2. Test with small positions first
3. Monitor data: do scaled positions outperform?
4. Adjust thresholds based on results

**Safety:**
- All existing duplicate prevention logic intact
- Flip logic unchanged (still requires quality check)
- Position Manager tracks scaling state
- Can be toggled on/off without code changes

lib/trading/position-manager.ts

@@ -48,6 +48,11 @@ export interface ActiveTrade {
   maxFavorablePrice: number     // Price at best profit
   maxAdversePrice: number       // Price at worst loss
   
+  // Position scaling tracking
+  originalAdx?: number          // ADX at initial entry (for scaling validation)
+  timesScaled?: number          // How many times position has been scaled
+  totalScaleAdded?: number      // Total USD added through scaling
+  
   // Monitoring
   priceCheckCount: number
   lastPrice: number