fix: fix timezone handling across backend and frontend (v0.3.1)

- Add tz.py with local_strftime/to_local helpers that read system.timezone
  from DB and convert UTC datetimes to venue local time before formatting
- Fix all strftime() calls in orders.py, reports.py, printer_service.py
  that were formatting UTC datetimes without timezone conversion
- Fix get_order endpoint returning raw dicts without Z suffix on datetimes,
  causing JS new Date() to treat timestamps as local instead of UTC
- Fix fmtDate() in tokens.js that stripped the T separator before parsing,
  breaking UTC-to-local conversion for all report date displays
- Make open/partially_paid table chips more visually distinct on dashboard

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

local_backend/services/printer_service.py

@@ -18,6 +18,7 @@ from sqlalchemy.orm import Session
 
 from database import SessionLocal
 from models.order import Order, OrderItem, PrintLog
+from tz import to_local
 from models.printer import Printer
 from models.product import Product
 from models.settings import PosSettings
@@ -232,8 +233,8 @@ def _print_line(p: Network, text: str, size: int, bold: bool, caps: bool,
 
 
 def _greek_date(dt: datetime.datetime) -> str:
-    """Return date/time string in Greek format: HH:MM DD-MM-YYYY"""
-    return dt.strftime("%H:%M  %d-%m-%Y")
+    """Return date/time string in Greek format: HH:MM DD-MM-YYYY, converted to venue local time."""
+    return to_local(dt).strftime("%H:%M  %d-%m-%Y")
 
 
 def check_printer(ip: str, port: int) -> bool:
@@ -282,7 +283,7 @@ def send_test_print(ip: str, port: int, name: str) -> Tuple[bool, str]:
         p._raw(b'\x1b\x21\x30')
         _raw_text(p, f"TEST — {name}\n")
         p._raw(b'\x1b\x21\x00')
-        now = datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")
+        now = to_local(datetime.datetime.now(datetime.timezone.utc)).strftime("%Y-%m-%d %H:%M:%S")
         _raw_text(p, f"{now}\n")
         p._raw(b'\n\n\n')
         p.cut()
@@ -499,7 +500,7 @@ def _print_kitchen_ticket(p: Network, order: Order, items: List[OrderItem], db:
     # Resolve display names
     table_name  = order.table.label or str(order.table.number) if order.table else str(order.table_id)
     waiter_nick = (order.opener.nickname or order.opener.username) if order.opener else str(order.opened_by)
-    now_str     = _greek_date(datetime.datetime.now())
+    now_str     = _greek_date(datetime.datetime.now(datetime.timezone.utc))
 
     # ── COMPACT header — single line ────────────────────────────────────────
     if compact: