fix: Resolve v1.1.2-rc.1 production issues - Static files and metrics

This release candidate fixes two critical production issues discovered in v1.1.2-rc.1:

1. CRITICAL: Static files returning 500 errors
   - HTTP monitoring middleware was accessing response.data on streaming responses
   - Fixed by checking direct_passthrough flag before accessing response data
   - Static files (CSS, JS, images) now load correctly
   - File: starpunk/monitoring/http.py

2. HIGH: Database metrics showing zero
   - Configuration key mismatch: config set METRICS_SAMPLING_RATE (singular),
     buffer read METRICS_SAMPLING_RATES (plural)
   - Fixed by standardizing on singular key name
   - Modified MetricsBuffer to accept both float and dict for flexibility
   - Changed default sampling from 10% to 100% for better visibility
   - Files: starpunk/monitoring/metrics.py, starpunk/config.py

Version: 1.1.2-rc.2

Documentation:
- Investigation report: docs/reports/2025-11-28-v1.1.2-rc.1-production-issues.md
- Architect review: docs/reviews/2025-11-28-v1.1.2-rc.1-architect-review.md
- Implementation report: docs/reports/2025-11-28-v1.1.2-rc.2-fixes.md

Testing: All monitoring tests pass (28/28)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

starpunk/monitoring/http.py

@@ -72,7 +72,15 @@ def setup_http_metrics(app: Flask) -> None:
 
         # Get response size
         response_size = 0
-        if response.data:
+
+        # Check if response is in direct passthrough mode (streaming)
+        if hasattr(response, 'direct_passthrough') and response.direct_passthrough:
+            # For streaming responses, use content_length if available
+            if hasattr(response, 'content_length') and response.content_length:
+                response_size = response.content_length
+            # Otherwise leave as 0 (unknown size for streaming)
+        elif response.data:
+            # For buffered responses, we can safely get the data
             response_size = len(response.data)
         elif hasattr(response, 'content_length') and response.content_length:
             response_size = response.content_length