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>

CLAUDE.md

@@ -64,7 +64,7 @@ make web-debug    # Same with FLASK_DEBUG=1
 make test         # Run all tests (unittest discover)
 make test-v       # Tests with verbose output
 make fees         # Print fee report from attendance sheet
-make sync-2026    # Sync Fio bank transactions for 2026 to Google Sheets
+make sync-year    # Sync Fio transactions for the current year plus Nov-Dec of the previous one (YEAR=N to override)
 make infer        # Auto-fill Person/Purpose/Amount columns in payments sheet
 make reconcile    # Print balance report from Google Sheets data
 make image        # Build the legacy Python Docker image