feat(dolt): migration 026 + models — fundamentals/earnings schema (A1 schema)

First reviewable slice of workstream A: schema only, no importers, no data.

- data_import_runs: lean batch-import audit (source/revision/status,
  row_counts_json + validation_json as Text-holding-JSON per repo convention).
- fundamental_snapshots: CIK-keyed, one immutable row per accession; stores
  per-period raw facts (duration = cumulative YTD/FY, balance-sheet =
  period-end) plus period_start/period_end/fiscal_year/fiscal_period so
  discrete quarters, Q4, TTM and YoY are derived at read time.
- earnings_events: Dolt-sourced calendar + surprise history, unique
  (ticker_id, announce_date).
- tickers: nullable cik/sic/sic_description — the ticker<->issuer join point.

fundamental_data is left untouched (cutover gated separately at A5). Models
registered in app/models/__init__.py; Ticker gains an earnings_events
relationship. Verified: create_all builds the tables, mappers configure, and
migration 026 renders valid Postgres DDL up and down.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/models/__init__.py

@@ -3,6 +3,9 @@ from app.models.ohlcv import OHLCVRecord
 from app.models.user import User
 from app.models.sentiment import SentimentScore
 from app.models.fundamental import FundamentalData
+from app.models.fundamental_snapshot import FundamentalSnapshot
+from app.models.earnings_event import EarningsEvent
+from app.models.data_import_run import DataImportRun
 from app.models.score import DimensionScore, CompositeScore
 from app.models.sr_level import SRLevel
 from app.models.trade_setup import TradeSetup
@@ -21,6 +24,9 @@ __all__ = [
     "User",
     "SentimentScore",
     "FundamentalData",
+    "FundamentalSnapshot",
+    "EarningsEvent",
+    "DataImportRun",
     "DimensionScore",
     "CompositeScore",
     "SRLevel",