dbs: add last_seen column to proxylist

dbs.py

@@ -88,6 +88,16 @@ def _migrate_protos_working(sqlite):
         sqlite.commit()
 
 
+def _migrate_last_seen(sqlite):
+    """Add last_seen column for worker-reported proxy freshness tracking."""
+    try:
+        sqlite.execute('SELECT last_seen FROM proxylist LIMIT 1')
+    except Exception:
+        # last_seen: unix timestamp of most recent "working" report from any worker
+        sqlite.execute('ALTER TABLE proxylist ADD COLUMN last_seen INT DEFAULT 0')
+        sqlite.commit()
+
+
 def compute_proxy_list_hash(proxies):
     """Compute MD5 hash of sorted proxy list for change detection.
 
@@ -315,7 +325,8 @@ def create_table_if_not_exists(sqlite, dbname):
             confidence INT DEFAULT 30,
             source_proto TEXT,
             source_confidence INT DEFAULT 0,
-            protos_working TEXT)""")
+            protos_working TEXT,
+            last_seen INT DEFAULT 0)""")
         # Migration: add columns to existing databases (must run before creating indexes)
         _migrate_latency_columns(sqlite)
         _migrate_anonymity_columns(sqlite)
@@ -324,6 +335,7 @@ def create_table_if_not_exists(sqlite, dbname):
         _migrate_confidence_column(sqlite)
         _migrate_source_proto(sqlite)
         _migrate_protos_working(sqlite)
+        _migrate_last_seen(sqlite)
         # Indexes for common query patterns
         sqlite.execute('CREATE INDEX IF NOT EXISTS idx_proxylist_failed ON proxylist(failed)')
         sqlite.execute('CREATE INDEX IF NOT EXISTS idx_proxylist_tested ON proxylist(tested)')