fix(decision): correct Unicode regex escaping in reInvisibleRunes

## Critical Fix

### Problem
- ❌ `regexp.MustCompile(`[\u200B...]`)` (backticks = raw string)
- Raw strings don't parse \uXXXX escape sequences in Go
- Regex was matching literal text "\u200B" instead of Unicode characters

### Solution
- ✅ `regexp.MustCompile("[\u200B...]")` (double quotes = parsed string)
- Double quotes properly parse Unicode escape sequences
- Now correctly matches U+200B (zero-width space), U+200C, U+200D, U+FEFF

## Impact
- Zero-width characters are now properly removed before JSON parsing
- Prevents invisible character corruption in AI responses
- Fixes potential JSON parsing failures

## Related
- Same fix applied to z-dev in commit db7c035

decision/engine.go

@@ -20,7 +20,7 @@ var (
 	reJSONArray      = regexp.MustCompile(`(?is)\[\s*\{.*?\}\s*\]`)
 	reArrayHead      = regexp.MustCompile(`^\[\s*\{`)
 	reArrayOpenSpace = regexp.MustCompile(`^\[\s+\{`)
-	reInvisibleRunes = regexp.MustCompile(`[\u200B\u200C\u200D\uFEFF]`)
+	reInvisibleRunes = regexp.MustCompile("[\u200B\u200C\u200D\uFEFF]")
 )
 
 // PositionInfo 持仓信息