Apply velvet-table redesign, fix game lifecycle and history bugs

Frontend:
- Dark green/gold "velvet table" visual redesign across the whole app
  (Auth, Lobby, GameList, GameTable, History, GameOver, modals), with
  Playfair Display/DM Sans typography and a centralized Tailwind palette.
- Desktop game table fit-scales to fill the window; mobile gets
  overlapping hand/trick layouts and larger touch-friendly cards.
- Standings sidebar now groups completed rounds by series with a
  per-series subtotal row, struck-through tips on missed bids.
- History page rewritten into a scoreboard-style detail view (player
  totals beside names, series grouped 2-up on desktop / stacked on
  mobile) and gained game names, completed/abandoned status, and a
  button to reopen a prematurely-ended game back into the lobby.

Backend:
- Fix started games being deleted from memory (and vanishing from
  everyone's lobby) when all players disconnect; only `end_game` tears
  down a started game now.
- Fix a crash writing a timezone-aware datetime into the naive
  `ended_at` Postgres column.
- Add `reopen_game`/`restore_game` to un-end a prematurely-ended game
  from history and resume it from the lobby.
- Let any seated player end an abandoned game once the host is
  offline, not just the host, so the game isn't stuck forever.
- Expose SERIES_PER_GAME/ROUNDS_PER_SERIES as named constants on the
  engine so the persistence layer derives game-completion rules from
  bridzik.py instead of re-encoding them.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

bridzik.py

@@ -82,6 +82,13 @@ class Card():
 cards = [Card(color, value) for value in Card_values for color in Card_colors]
 
 
+# Sturktura hry: kazda hra ma SERIES_PER_GAME serii, kazda seria ma
+# ROUNDS_PER_SERIES kol. Jediny zdroj pravdy pre tieto cisla -- ina vrstva
+# (napr. api/history.py) ich odvodzuje odtialto, nikdy si ich nevymysla sama.
+SERIES_PER_GAME = 4
+ROUNDS_PER_SERIES = 8
+
+
 class Bridzik():
     def __init__(self, shuffler=shuffle):
         self.shuffler = shuffler
@@ -124,7 +131,7 @@ class Bridzik():
         return status
 
     def is_completed(self):
-        return len(self.series) == 4 and self.series[-1].is_completed()
+        return len(self.series) == SERIES_PER_GAME and self.series[-1].is_completed()
 
     def get_previous_stash(self):
         if len(self.series[-1].get_last_round().stashes) > 1:
@@ -169,7 +176,7 @@ class Series():
             self.start_new_round()
 
     def is_completed(self):
-        return len(self.rounds) == 8 and self.get_last_round().is_completed()
+        return len(self.rounds) == ROUNDS_PER_SERIES and self.get_last_round().is_completed()
 
     def get_standings(self):
         return [r.get_points_summary() for r in self.rounds if r.is_completed()]
@@ -191,7 +198,7 @@ class Series():
 class Round():
     def __init__(self, round_number: int, first_player: int, cards: []=cards, shuffler=shuffle):
         # vyrob kopku pre toto kolo a priprav prazdne objekty
-        if round_number not in [i for i in range(8)]:
+        if round_number not in range(ROUNDS_PER_SERIES):
             raise BridzikException('Neplatne cislo kola.')
         if first_player not in [0, 1, 2, 3]:
             raise BridzikException('Cislo hraca musi byt 0, 1, 2 alebo 3.')