feat: shadow book + shadow-vs-manual performance comparison

The manual paper book only contains trades taken by hand, inside a 20
minute window, on days someone was available. The backtest that validated
this strategy auto-takes the top-ranked qualified setups up to capacity
every session. The forward record was therefore measuring strategy plus
discretion plus availability -- and degrading silently on busy days.

The shadow book closes that gap: it mirrors the backtest's selection rule
(top strategy_rank qualified, up to capacity, 1% fixed-fractional risk)
and shares the manual book's exit policy, so the only difference between
the two books is which setups get taken. Selection ordering reuses the
strategy_rank the scanner already stores rather than recomputing it, so
the two cannot drift apart. It runs as a near-close pipeline step right
after the scan, marking entries at the same prices a human would see.

Gate-reset re-entry state is now scoped per book -- the books diverge as
soon as their entries differ, and each must see only its own stops.

Performance view rewritten around the comparison:
  - three series (shadow, manual, SPY) from a new endpoint
  - SPY changes from a per-trade cost-basis counterfactual to plain
    buy-and-hold %, since one line has to serve two books
  - headline stats are R-multiples, not currency: the books size
    differently, so only R compares across them
  - configurable start date, because the strategy has been revised
    repeatedly and pre-cutover trades ran under rules that no longer
    exist

Migration 024 also repairs the numeric weekday crons written by 023,
rewriting only rows still holding the broken form so hand-corrected
settings survive. Its literals are inlined because bound parameters
render as NULL under 'alembic upgrade --sql'.

The shadow book is opt-in and writes nothing until enabled. Verify its
first selections match a backtest of that day's cross-section before
trusting any point on the curve.

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

alembic/versions/024_paper_trade_book.py

@@ -0,0 +1,59 @@
+"""paper trade book tag (manual vs shadow) + weekday cron repair
+
+Revision ID: 024
+Revises: 023
+Create Date: 2026-07-20 00:00:00.000000
+
+Two things ship together because both are corrections to 023's stored state.
+
+1. ``paper_trades.book`` separates the discretionary book from the automatic
+   shadow book. Everything that exists today was opened by hand, so the
+   backfill value is "manual".
+
+2. 023 wrote weekday crons with a numeric day-of-week. APScheduler's
+   from_crontab() feeds field 5 to its own day_of_week where 0=Monday, so
+   "1-5" resolved to Tue-Sat: every Monday was skipped and the scanner ran on
+   Saturdays against stale data. Rewrite only the rows that still hold the
+   broken numeric form, so a hand-corrected setting is never clobbered.
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision: str = "024"
+down_revision: Union[str, None] = "023"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+# key -> (broken numeric form written by 023, corrected named form)
+_CRON_REPAIR: dict[str, tuple[str, str]] = {
+    "schedule_near_close_pipeline_cron": ("30 15 * * 1-5", "30 15 * * mon-fri"),
+    "schedule_after_close_pipeline_cron": ("45 16 * * 1-5", "45 16 * * mon-fri"),
+    "schedule_intraday_pipeline_cron": ("0 10-15 * * 1-5", "0 10-15 * * mon-fri"),
+    "schedule_fundamentals_cron": ("0 1 * * 1", "0 1 * * mon"),
+}
+
+
+def upgrade() -> None:
+    # server_default backfills existing rows, so no separate UPDATE is needed.
+    op.add_column(
+        "paper_trades",
+        sa.Column("book", sa.String(length=10), nullable=False, server_default="manual"),
+    )
+
+    # Literals are inlined rather than bound because bound parameters render as
+    # NULL under `alembic upgrade --sql`, which would silently produce a script
+    # that matches nothing. Every value here is a constant defined above.
+    for key, (broken, fixed) in _CRON_REPAIR.items():
+        op.execute(
+            f"UPDATE system_settings SET value = '{fixed}' "  # noqa: S608
+            f"WHERE key = '{key}' AND value = '{broken}'"
+        )
+
+
+def downgrade() -> None:
+    op.drop_column("paper_trades", "book")
+    # Crons are deliberately left corrected — restoring the numeric form would
+    # reintroduce the skipped-Monday bug.