Add draw_animation_seconds config and expose winner info during a round

RoundConfig gains draw_animation_seconds (default 20) — the minimum
time the frontend's "estrazione in corso" animation plays before
revealing a winner. It's purely a UI cue: the real draw still waits for
a confirmed block for its entropy (rounds/scheduler.py), which usually
takes much longer than this value, so it only ever extends the
animation, never truncates the real wait.

GET /rounds/current now also returns draw_animation_seconds,
winner_user_id and winner_amount_sats (all populated once the
scheduler sets them on the round, i.e. from "paying_out" onward) so a
client can determine and reveal the outcome. GET /users/me now returns
the user's own id, needed client-side to compare against winner_user_id.

Admin config CRUD refactored to a shared field tuple (_CONFIG_FIELDS)
instead of repeating the same 7-then-8 field list three times.

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

app/db/models.py

@@ -87,6 +87,11 @@ class RoundConfig(Base):
     bet_amount_sats: Mapped[int] = mapped_column(BigInteger, default=1_000_000_000)
     round_duration_seconds: Mapped[int] = mapped_column(default=600)
     round_cooldown_seconds: Mapped[int] = mapped_column(default=30)
+    # Purely a frontend cue: the minimum time the "estrazione in corso" animation
+    # plays for on every user's dashboard before the winner can be revealed. Does
+    # NOT gate the actual draw, which still waits for a real confirmed block for
+    # its entropy (rounds/scheduler.py) — that can take longer than this value.
+    draw_animation_seconds: Mapped[int] = mapped_column(default=20)
     min_amount_sats: Mapped[int] = mapped_column(BigInteger, default=100_000_000)
     fee_rate_sat_vb: Mapped[int] = mapped_column(default=1)
     rbf_timeout_seconds: Mapped[int] = mapped_column(default=900)