Reliability improvements: retry logic, validation, ratings sync

- Add 3-attempt retry with exponential backoff to Sreality, Realingo,
  Bezrealitky, and PSN scrapers (CityHome and iDNES already had it)
- Add shared validate_listing() in scraper_stats.py; all 6 scrapers now
  validate GPS bounds, price, area, and required fields before output
- Wire ratings to server /api/ratings on page load (merge with
  localStorage) and save (async POST); ratings now persist across
  browsers and devices
- Namespace JS hash IDs as {source}_{id} to prevent rating collisions
  between listings from different portals with the same numeric ID
- Replace manual Czech diacritic table with unicodedata.normalize()
  in merge_and_map.py for correct deduplication of all edge cases
- Correct README schedule docs: every 4 hours, not twice daily

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scrape_psn.py

@@ -15,7 +15,7 @@ import time
 from datetime import datetime
 from pathlib import Path
 from urllib.parse import urlencode
-from scraper_stats import write_stats
+from scraper_stats import write_stats, validate_listing
 
 STATS_FILE = "stats_psn.json"
 
@@ -38,19 +38,25 @@ BASE_URL = "https://psn.cz"
 UNITS_API = f"{BASE_URL}/api/units-list"
 
 
-def fetch_json(url: str) -> dict:
-    """Fetch JSON via curl (urllib SSL may fail on Cloudflare)."""
-    logger.debug(f"HTTP GET: {url}")
-    result = subprocess.run(
-        ["curl", "-s", "-L", "--max-time", "30",
-         "-H", f"User-Agent: {UA}",
-         "-H", "Accept: application/json",
-         url],
-        capture_output=True, text=True, timeout=60
-    )
-    if result.returncode != 0:
-        raise RuntimeError(f"curl failed ({result.returncode}): {result.stderr[:200]}")
-    return json.loads(result.stdout)
+def fetch_json(url: str, retries: int = 3) -> dict:
+    """Fetch JSON via curl (urllib SSL may fail on Cloudflare) with retry."""
+    for attempt in range(retries):
+        logger.debug(f"HTTP GET (attempt {attempt + 1}/{retries}): {url}")
+        result = subprocess.run(
+            ["curl", "-s", "-L", "--max-time", "30",
+             "-H", f"User-Agent: {UA}",
+             "-H", "Accept: application/json",
+             url],
+            capture_output=True, text=True, timeout=60
+        )
+        if result.returncode == 0:
+            return json.loads(result.stdout)
+        if attempt < retries - 1:
+            wait = (attempt + 1) * 2
+            logger.warning(f"curl failed (retry {attempt + 1}/{retries} after {wait}s): {result.stderr[:200]}")
+            time.sleep(wait)
+        else:
+            raise RuntimeError(f"curl failed after {retries} attempts ({result.returncode}): {result.stderr[:200]}")
 
 
 def fix_gps(lat, lng):
@@ -255,6 +261,8 @@ def scrape(max_properties: int | None = None):
             "first_seen": _prev_cache.get(str(unit_id), {}).get("first_seen", datetime.now().strftime("%Y-%m-%d")),
             "last_changed": datetime.now().strftime("%Y-%m-%d") if _prev_cache.get(str(unit_id), {}).get("price") != int(price) else _prev_cache[str(unit_id)].get("last_changed", datetime.now().strftime("%Y-%m-%d")),
         }
+        if not validate_listing(result, "psn"):
+            continue
         results.append(result)
         properties_fetched += 1