fix: select shadow book setups by scan run id, not a time window

The run-id marker proved which scan wrote last, but the shadow book still
selected setups by detected_at >= scan_start. An overlapping manual scan
could insert rows in that same window; if the pipeline's scan wrote the
marker last its id matched and the shadow book proceeded, then swept in --
or ranked highest -- a manual-scan row. The identity check gated entry but
selection did not.

Carry the run id onto the rows. Migration 025 adds an indexed
trade_setups.scan_run_id. scan_all_tickers computes one id per run
(pipeline's when a step, else fresh), passes it to scan_ticker which stamps
every row after enhancement, and writes the same id to the completion
marker. The shadow book selects WHERE scan_run_id == the matched id, so a
concurrent scan's rows are excluded by identity regardless of their
detected_at. The now-unused STARTED marker is dropped; COMPLETED
(freshness) and RUN_ID (identity) remain.

Decisive test: the pipeline's id matches, but a same-window manual row with
a higher rank is present and is excluded -- only the pipeline's own row is
traded. A time-window select would have swept it in and ranked it first.

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

app/models/trade_setup.py

@@ -45,6 +45,11 @@ class TradeSetup(Base):
         DateTime(timezone=True), nullable=True
     )
     outcome_date: Mapped[date | None] = mapped_column(Date, nullable=True)
+    # Identity of the scan run that produced this row. The shadow book selects
+    # its batch by this id, not by a detected_at window, so a concurrent manual
+    # scan writing rows in the same time window is excluded by identity. Null on
+    # rows predating the column and on any non-scan creator.
+    scan_run_id: Mapped[str | None] = mapped_column(String(32), nullable=True)
 
     ticker = relationship("Ticker", back_populates="trade_setups")