feat(observability): structured logging, metrics wiring, graceful degradation

- Item 5: Convert remaining printf-style logger call to structured logging
  (key=value format) in x402_middleware.py
- Item 6: Wire CACHE_HITS counter into cache get() and per-tier SCRAPE_LATENCY
  histogram into UltimateScraper scrape loop
- Item 7: Add circuit-breaker checks in extractor.py (Ollama) and
  routers/vision.py (OpenRouter) to fail fast and record success/failure
  when external services are down; attach recovery results to resilience
  registry for per-service circuit state

560 tests passing, ruff clean

cache.py

@@ -12,6 +12,8 @@ import json
 import time
 from collections import OrderedDict
 
+from observability import CACHE_HITS
+
 
 class ResponseCache:
     """Two-tier cache: local LRU + optional Redis persistence.
@@ -44,6 +46,8 @@ class ResponseCache:
             if entry["expires"] > now:
                 self._hits += 1
                 self._cache.move_to_end(key)
+                if CACHE_HITS:
+                    CACHE_HITS.labels(cache_type="local").inc()
                 return entry["data"]
             else:
                 del self._cache[key]