fix: remove FIRST early return that also blocked re-extraction

There were TWO `if not unprocessed: return 0, 0` gates. The previous
fix (c763c99) only addressed the second one. The first at line 746
fires before the re-extraction query even runs. Replace with a comment
explaining why we don't early-return there.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/extract.py

@@ -743,8 +743,8 @@ async def extract_cycle(conn, max_workers=None) -> tuple[int, int]:
         except Exception:
             logger.debug("Failed to read source %s", f, exc_info=True)
 
-    if not unprocessed:
-        return 0, 0
+    # Don't early-return here — re-extraction sources may exist even when queue is empty
+    # (the re-extraction check runs after open-PR filtering below)
 
     # Filter out sources that already have open extraction PRs
     open_pr_slugs = set()