Retire in-code comments that outlived what they described (B-69)

- app/tx/reconcile.py called the payout retry "a future payout-retry
  routine — still an open gap". It shipped as B-26: clearing payout_txid
  leaves the round in exactly the state _retry_payout_if_due picks up, so
  an abandoned payout rebuilds itself and the log line next to it is an
  alert, not the recovery path. Reading it the old way, an operator would
  go hand-fix a round the scheduler was already retrying.
- app/db/base.py sized the SQLite busy timeout against "five concurrent
  background tasks" and then listed only the non-listener ones; the
  lifespan starts six.
- The third item (app/auth/routes.py citing B-31 where it meant B-33) was
  already correct in the tree; the test pins it so it stays that way.

tests/unit/test_code_comments.py derives the task count from the lifespan's
own create_task calls rather than restating it, so the comment fails the
next time a task is added or removed instead of quietly going stale again.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app/db/base.py

@@ -6,8 +6,9 @@ from app.config import settings
 
 # How long a writer waits for a lock held by another writer before SQLite raises
 # "database is locked" (B-39). A few seconds is enough to ride out this app's own
-# five concurrent background tasks (scheduler, confirmation poller, RBF bumper,
-# two reconcilers) plus HTTP handlers briefly overlapping a write.
+# six concurrent background tasks (Electrum listener, scheduler, confirmation
+# poller, RBF bumper, two reconcilers) plus HTTP handlers briefly overlapping a
+# write.
 _SQLITE_BUSY_TIMEOUT_MS = 5000