feat(tickers): record delisting instead of deleting the symbol

Retiring a symbol meant delete_ticker or bootstrap_universe(prune_missing),
both of which cascade through OHLCV, setups and scores. That destroys exactly
the history four research documents already apologise for: today's tracked
universe projected backward is survivorship-biased, and hard-deleting every
delisted name is what causes it. Keeping the rows preserves the option to fix
that — it does not fix it, which needs the replay to model a delisting as an
exit event.

tickers gains delisted_on / delisted_reason (migration 032). NULL means
actively traded.

The filter is opt-in via ticker_service.active_only rather than folded into a
shared getter: the registry and admin views deliberately keep delisted rows so
the delisting is visible, and a silent default would undo that. Applied to the
live path only — scanner, momentum ranking, scoring, breadth, fundamentals
candidates, SEC universe, earnings import, ingestion loops. run_backtest keeps
them on purpose.

Detection runs off OHLCV staleness, not off the SEC fundamentals import: that
importer stalls for days on unrelated Company-Facts gaps and would take
detection down with it. On a stale symbol the scheduler asks SEC for a Form
25/25-NSE/15 and retires it only on a hit, so a halt or a rename (SATS->ECHO)
keeps the existing warning. The probe waits 3 stale days so a market-data
outage cannot turn into one SEC request per symbol per run.

Safe to automate because it is reversible: clear_delisted un-retires a false
positive, where a delete had already taken the history.

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

app/services/dolt_earnings_importer.py

@@ -32,7 +32,7 @@ from app.config import settings
 from app.database import insert_for_session
 from app.models.earnings_event import EarningsEvent
 from app.models.ticker import Ticker
-from app.services import dolt_client, earnings_alignment
+from app.services import dolt_client, earnings_alignment, ticker_service
 from app.services.data_import import ValidationResult
 
 logger = logging.getLogger(__name__)
@@ -289,7 +289,11 @@ class DoltEarningsImporter:
     # -- helpers -----------------------------------------------------------
 
     async def _load_universe(self, db) -> dict[str, int]:
-        rows = (await db.execute(select(Ticker.id, Ticker.symbol))).all()
+        rows = (
+            await db.execute(
+                ticker_service.active_only(select(Ticker.id, Ticker.symbol))
+            )
+        ).all()
         return {
             earnings_alignment.normalise_symbol(symbol): tid
             for tid, symbol in rows