fix: harden shadow book against book leakage (review of ba2df8b)

Review of the shadow book found seven ways the two books could leak into
each other; all are fixed here. The most serious silently invalidated the
comparison the shadow book exists to make.

- Shadow holdings no longer suppress the manual candidate list. The
  open-trade exclusion filtered on any book, so shadow taking the
  top-ranked names removed exactly those from the user's list and alerts,
  confining the discretionary book to leftovers. Scoped to the manual
  book. Closed-trade alerts and paper-book equity were leaking the same
  way and are likewise scoped.

- Shadow sizing now matches _simulate_portfolio: min(1% risk, 20% notional
  cap, available cash) from marked equity, plus the sub- dust guard.
  Previously risk-only from realized equity, so a tight stop produced a
  multiples-of-equity leveraged position the strategy would never take.

- Shadow only trades setups from the scan that just ran (<6h old) with one
  setup per ticker. A failed or disabled scan step could otherwise open
  positions from a prior session at stale prices.

- Gate-reset transitions are observed for both books, so a shadow stop-out
  completes fail -> requalify instead of staying locked forever.

- Manual list/close endpoints default to the manual book and reject
  hand-closing shadow trades; the performance endpoint is scoped to the
  caller so 'your picks' is not every user's book.

- run_shadow_book is registered as a paused job so Admin can trigger it.

Also anchors three pre-existing paper-trade tests (and the new alpaca
window test) on the UTC date. They build fixtures from the local date but
the service stamps opened_at in UTC, so they failed only between 00:00 and
02:00 in a UTC+hh timezone -- latent on ba2df8b, exposed by the clock.

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

app/services/paper_trade_service.py

@@ -402,7 +402,15 @@ async def list_trades(
     db: AsyncSession,
     user_id: int | None = None,
     status: str | None = None,
+    book: str | None = MANUAL_BOOK,
 ) -> list[dict]:
+    """Trades for the UI. Defaults to the discretionary book.
+
+    Shadow trades are attached to a user row for FK reasons only — they are not
+    that person's decisions. Listing them alongside manual trades would mix two
+    different books in one P&L and let the autonomous record be edited by hand.
+    Pass ``book=None`` to deliberately span both.
+    """
     stmt = (
         select(PaperTrade, Ticker.symbol)
         .join(Ticker, PaperTrade.ticker_id == Ticker.id)
@@ -411,6 +419,8 @@ async def list_trades(
         stmt = stmt.where(PaperTrade.user_id == user_id)
     if status is not None:
         stmt = stmt.where(PaperTrade.status == status)
+    if book is not None:
+        stmt = stmt.where(PaperTrade.book == book)
     stmt = stmt.order_by(PaperTrade.opened_at.desc())
 
     rows = (await db.execute(stmt)).all()
@@ -493,6 +503,13 @@ async def close_trade(
     trade = result.scalar_one_or_none()
     if trade is None:
         raise NotFoundError(f"Paper trade not found: {trade_id}")
+    if trade.book == SHADOW_BOOK:
+        # The shadow book's value is that no human touched it. A hand-closed
+        # position would make its record something other than what the strategy
+        # would have done; it exits only via the automatic exit policy.
+        raise ValidationError(
+            "Shadow book trades are closed by the exit policy, not by hand"
+        )
     if trade.status == "closed":
         raise ValidationError("Trade is already closed")
 
@@ -811,7 +828,7 @@ def _cumulative_pnl(trades: list, ticker_closes: dict, days: list[date]) -> list
     return out
 
 
-async def performance_summary(db: AsyncSession) -> dict:
+async def performance_summary(db: AsyncSession, user_id: int | None = None) -> dict:
     """Shadow book vs discretionary book vs SPY, from the configured start date.
 
     Currency P&L is reported per book but is *not* the comparison — the books
@@ -823,6 +840,12 @@ async def performance_summary(db: AsyncSession) -> dict:
     stmt = select(PaperTrade)
     if start is not None:
         stmt = stmt.where(func.date(PaperTrade.opened_at) >= start)
+    if user_id is not None:
+        # "Your picks" must be *yours*. The shadow book is a single autonomous
+        # book with no owner, so it is never scoped to a user.
+        stmt = stmt.where(
+            (PaperTrade.book == SHADOW_BOOK) | (PaperTrade.user_id == user_id)
+        )
     trades = list((await db.execute(stmt)).scalars().all())
 
     benchmark_closes = await benchmark_service.load_benchmark_closes(db)