fix(sync): dashboard sync covers current year plus Nov-Dec of previous

/sync-bank now uses one shared default window in both implementations:
1 November of the previous year to 31 December of the current year.
Payments dated around New Year are picked up in January; duplicates
are still filtered by Sync ID.

Python used a hardcoded 2026 window and would have stopped syncing on
2027-01-01; Go used the current calendar year only.

Adds make sync-year [YEAR=N] with the same window. The CLI default
without flags (last 30 days) is unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

legacy/scripts/sync_fio_to_sheets.py

@@ -59,6 +59,18 @@ def get_sheets_service(credentials_path: str):
     return _SHEETS_SERVICE
 
 
+def default_sync_window(today=None) -> tuple[str, str]:
+    """Window used by the dashboard sync, as (from, to) in YYYY-MM-DD.
+
+    The whole current calendar year plus the last two months of the previous
+    one, so payments dated around New Year are still picked up in January.
+    Re-fetching is safe because rows are deduplicated by Sync ID.
+    Mirrors DefaultWindow in go/internal/services/banksync/sync.go.
+    """
+    year = (today or datetime.now()).year
+    return f"{year - 1}-11-01", f"{year}-12-31"
+
+
 def as_text_cell(value) -> str:
     """Mark a value to be stored as text when written with USER_ENTERED.