feat(dolt): add shares_outstanding_date to fundamental_snapshots (026)

A1 carry-forward. The SEC cover-page share count
(dei:EntityCommonStockSharesOutstanding) is reported "as of" its own date, which
can differ from the fiscal period_end — store that date so market cap uses the
right point-in-time count. Migration 026 edited in place (never run with data).

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

alembic/versions/026_dolt_fundamentals_schema.py

@@ -66,6 +66,7 @@ def upgrade() -> None:
         sa.Column("cash_and_st_investments", sa.Float(), nullable=True),
         sa.Column("total_debt", sa.Float(), nullable=True),
         sa.Column("shares_outstanding", sa.Float(), nullable=True),
+        sa.Column("shares_outstanding_date", sa.Date(), nullable=True),
         sa.Column(
             "import_run_id",
             sa.Integer(),