fix(python): parse Fio 2-digit-year dates + add make sync-debug

Fio's transparent page now serves recent rows as DD.MM.YY while older
rows stay DD.MM.YYYY. parse_czech_date only knew the 4-digit form so
every recent transfer was silently dropped — make sync-2026 reported
zero new transactions. Adds %d.%m.%y and %d/%m/%y to the format list,
mirroring the Go-side fix from 2026-05-07.

Also adds a Python analog of make go-sync-debug:
- --dry-run skips header write / append / sort and prints "would …" lines
- --print-fio-table prints aligned per-txn table with NEW/DUP status
- make sync-debug [DAYS=N] wrapper (default DAYS=30)
- always-on stderr diagnostics in fio_utils: which fetcher was chosen
  (with FIO_API_TOKEN-unset lag warning) + raw-vs-filtered counts, so
  this class of "scraper drops everything" bug surfaces immediately.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## 2026-05-11 22:56 CEST — fix(python): parse Fio 2-digit-year dates + add `make sync-debug` dry-run tool
+
+- Fix: `scripts/fio_utils.py` `parse_czech_date` now accepts `DD.MM.YY` / `D.M.YY` in addition to the 4-digit-year variants. Fio's transparent page now mixes both forms in the same response; the 2-digit rows were being silently dropped, which caused `make sync-2026` to miss every recent transfer. Mirrors the Go-side fix from 2026-05-07 (CHANGELOG entry below).
+- Added `--dry-run` and `--print-fio-table` flags to `scripts/sync_fio_to_sheets.py`, plus a `make sync-debug [DAYS=N]` Makefile target. Mirrors `make go-sync-debug`: fetches from Fio and dedupes against the sheet, prints `STATUS=NEW/DUP` per transaction, and prints per-row `Dry run: would append …` lines + `would sort by date` instead of touching the sheet.
+- Added always-on stderr diagnostics in `scripts/fio_utils.py`: which fetcher was selected (authenticated API vs. transparent-page scraper with `FIO_API_TOKEN`-unset warning), and raw-vs-after-filter transaction counts on both paths — so this class of "scraper drops everything" bug surfaces immediately.
+
 ## 2026-05-08 14:55 CEST — feat(go): M6.6.1 — Pay-button QR popup modal
 
 - Restored the Python `showPayQR` in-page modal UX that was lost in M6.6 (Pay buttons were navigating the tab to the raw `/qr` PNG).