feat: Add multi-level confidence filtering for pattern detection (fixes #240)

## Problem
Pattern detection was producing too many low-confidence patterns:
- 905 patterns detected (overwhelming)
- Many with confidence as low as 0.50
- 4,875 lines in patterns index.md
- Low signal-to-noise ratio

## Solution

### 1. Added Confidence Thresholds (pattern_recognizer.py)
```python
CONFIDENCE_THRESHOLDS = {
    'critical': 0.80,   # High-confidence for ARCHITECTURE.md
    'high': 0.70,       # Detailed analysis
    'medium': 0.60,     # Include with warning
    'low': 0.50,        # Minimum detection
}
```

### 2. Created Filtering Utilities (pattern_recognizer.py:1650-1723)
- `filter_patterns_by_confidence()` - Filter by threshold
- `create_multi_level_report()` - Multi-level grouping with statistics

### 3. Multi-Level Output Files (codebase_scraper.py:1009-1055)
Now generates 4 output files:
- **all_patterns.json** - All detected patterns (unfiltered)
- **high_confidence_patterns.json** - Patterns ≥ 0.70 (for detailed analysis)
- **critical_patterns.json** - Patterns ≥ 0.80 (for ARCHITECTURE.md)
- **summary.json** - Statistics and thresholds

### 4. Enhanced Logging
```
✅ Detected 4 patterns in 1 files
   🔴 Critical (≥0.80): 0 patterns
   🟠 High (≥0.70): 0 patterns
   🟡 Medium (≥0.60): 1 patterns
   ⚪ Low (<0.60): 3 patterns
```

## Results

**Before:**
- Single output file with all patterns
- No confidence-based filtering
- Overwhelming amount of data

**After:**
- 4 output files by confidence level
- Clear quality indicators (🔴🟠🟡⚪)
- Easy to find high-quality patterns
- Statistics in summary.json

**Example Output:**
```json
{
  "statistics": {
    "total": 4,
    "critical_count": 0,
    "high_confidence_count": 0,
    "medium_count": 1,
    "low_count": 3
  },
  "thresholds": {
    "critical": 0.80,
    "high": 0.70,
    "medium": 0.60,
    "low": 0.50
  }
}
```

## Benefits

1. **Better Signal-to-Noise Ratio**
   - Focus on high-confidence patterns
   - Low-confidence patterns separate

2. **Flexible Usage**
   - ARCHITECTURE.md uses critical_patterns.json
   - Detailed analysis uses high_confidence_patterns.json
   - Debug/research uses all_patterns.json

3. **Clear Quality Indicators**
   - Visual indicators (🔴🟠🟡⚪)
   - Explicit thresholds documented
   - Statistics for quick assessment

4. **Backward Compatible**
   - all_patterns.json maintains full data
   - No breaking changes to existing code
   - Additional files are opt-in

## Testing

**Test project:**
```python
class SingletonDatabase:  # Detected with varying confidence
class UserFactory:        # Detected patterns
class Logger:             # Observer pattern (0.60 confidence)
```

**Results:**
- ✅ All 41 tests passing
- ✅ Multi-level filtering works correctly
- ✅ Statistics accurate
- ✅ Output files created properly

## Future Improvements (Not in this PR)

- Context-aware confidence boosting (pattern in design_patterns/ dir)
- Pattern count limits (top N per file/type)
- AI-enhanced confidence scoring
- Per-language threshold tuning

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/skill_seekers/cli/pattern_recognizer.py

@@ -28,6 +28,17 @@ from pathlib import Path
 
 logger = logging.getLogger(__name__)
 
+# Confidence thresholds for pattern filtering (Issue #240)
+CONFIDENCE_THRESHOLDS = {
+    'critical': 0.80,   # High-confidence patterns for ARCHITECTURE.md
+    'high': 0.70,       # Include in detailed analysis
+    'medium': 0.60,     # Include with warning/context
+    'low': 0.50,        # Minimum detection threshold
+}
+
+# Default minimum confidence for pattern detection
+DEFAULT_MIN_CONFIDENCE = CONFIDENCE_THRESHOLDS['low']
+
 
 @dataclass
 class PatternInstance:
@@ -1636,6 +1647,76 @@ class LanguageAdapter:
         return pattern
 
 
+# ============================================================================
+# PATTERN FILTERING UTILITIES (Issue #240 - C4.2)
+# ============================================================================
+
+
+def filter_patterns_by_confidence(patterns: list[dict], min_confidence: float) -> list[dict]:
+    """
+    Filter patterns by minimum confidence threshold.
+
+    Args:
+        patterns: List of pattern dictionaries (from PatternReport.to_dict())
+        min_confidence: Minimum confidence threshold (0.0-1.0)
+
+    Returns:
+        Filtered list of patterns meeting the threshold
+    """
+    filtered = []
+    for pattern in patterns:
+        if pattern.get("confidence", 0.0) >= min_confidence:
+            filtered.append(pattern)
+    return filtered
+
+
+def create_multi_level_report(pattern_results: list[dict]) -> dict:
+    """
+    Create multi-level pattern report with different confidence thresholds.
+
+    Args:
+        pattern_results: List of PatternReport dictionaries
+
+    Returns:
+        Dictionary with patterns grouped by confidence level:
+        - all_patterns: All detected patterns
+        - high_confidence: Patterns >= 0.70 (for detailed analysis)
+        - critical: Patterns >= 0.80 (for ARCHITECTURE.md)
+        - statistics: Pattern count by level
+    """
+    # Flatten all patterns from all files
+    all_patterns = []
+    for report in pattern_results:
+        file_path = report.get("file_path", "unknown")
+        for pattern in report.get("patterns", []):
+            # Add file path to pattern for context
+            pattern_with_file = {**pattern, "file_path": file_path}
+            all_patterns.append(pattern_with_file)
+
+    # Sort by confidence (highest first)
+    all_patterns_sorted = sorted(all_patterns, key=lambda p: p.get("confidence", 0.0), reverse=True)
+
+    # Filter by confidence levels
+    critical = filter_patterns_by_confidence(all_patterns_sorted, CONFIDENCE_THRESHOLDS['critical'])
+    high_confidence = filter_patterns_by_confidence(all_patterns_sorted, CONFIDENCE_THRESHOLDS['high'])
+    medium = filter_patterns_by_confidence(all_patterns_sorted, CONFIDENCE_THRESHOLDS['medium'])
+
+    return {
+        "all_patterns": all_patterns_sorted,
+        "critical": critical,
+        "high_confidence": high_confidence,
+        "medium": medium,
+        "statistics": {
+            "total": len(all_patterns_sorted),
+            "critical_count": len(critical),
+            "high_confidence_count": len(high_confidence),
+            "medium_count": len(medium),
+            "low_count": len(all_patterns_sorted) - len(medium),
+        },
+        "thresholds": CONFIDENCE_THRESHOLDS,
+    }
+
+
 def main():
     """
     CLI entry point for pattern detection.