docs: update roadmap with completed items

ROADMAP.md

@@ -179,14 +179,14 @@ PPF (Proxy Fetcher) is a Python 2 proxy scraping and validation framework design
 │                          │                                                  │
 │ [x] Unify _known_proxies │ [x] Connection pooling                           │
 │ [x] Graceful DB errors   │ [x] Dynamic thread scaling                       │
-│ [x] Batch inserts        │ [ ] Unit test infrastructure                     │
+│ [x] Batch inserts        │ [x] Unit test infrastructure                     │
 │ [x] WAL mode for SQLite  │ [x] Latency tracking                             │
 │                          │                                                  │
 ├──────────────────────────┼──────────────────────────────────────────────────┤
 │ LOW IMPACT / LOW EFFORT  │ LOW IMPACT / HIGH EFFORT                         │
 │                          │                                                  │
 │ [x] Standardize logging  │ [x] Geographic validation                        │
-│ [x] Config validation    │ [x] Additional scrapers                          │
+│ [x] Config validation    │ [x] Additional scrapers (Bing, Yahoo, Mojeek)    │
 │ [x] Export functionality │ [ ] API sources                                  │
 │ [x] Status output        │ [ ] Protocol fingerprinting                      │
 │                          │                                                  │
@@ -342,6 +342,7 @@ PPF (Proxy Fetcher) is a Python 2 proxy scraping and validation framework design
 - [x] Tab-aware chart rendering - skip expensive renders for hidden tabs
 - [x] Visibility API - pause polling when browser tab hidden
 - [x] Dark/muted-dark/light theme cycling
+- [x] Stats export endpoint (/api/stats/export?format=json|csv)
 
 ### Proxy Validation Cache (Done)
 - [x] LRU cache for is_usable_proxy() using OrderedDict
@@ -354,6 +355,20 @@ PPF (Proxy Fetcher) is a Python 2 proxy scraping and validation framework design
 - [x] Removed deprecated `_prep_db()` and `_close_db()` methods
 - [x] `fetch_rows()` now accepts db parameter for cleaner dependency injection
 
+### Additional Search Engines (Done)
+- [x] Bing and Yahoo engine implementations in scraper.py
+- [x] Engine rotation for rate limit avoidance
+- [x] engines.py module with SearchEngine base class
+
+### Worker Health Improvements (Done)
+- [x] Tor connectivity check before workers claim work
+- [x] Fixed interval Tor check (30s) instead of exponential backoff
+- [x] Graceful handling when Tor unavailable
+
+### Memory Optimization (Done)
+- [x] `__slots__` on ProxyTestState (27 attrs) and TargetTestJob (4 attrs)
+- [x] Reduced per-object memory overhead for hot path objects
+
 ---
 
 ## Technical Debt