feat(dolt): A2 — DoltHub earnings importer (shadow ingestion)

A SourceImporter that ingests post-no-preference/earnings into earnings_events
for the tracked universe. Shadow by construction (nothing reads earnings_events
until A4).

- earnings_alignment.py: pure calendar<->EPS-history min-cost monotonic DP,
  reused from scripts/import_dolthub_earnings.py with identical constants (not
  extending that one-off script); symbol/session normalization; unit-tested
  against the pinned constants.
- dolt_client.py: async dolt CLI wrapper (pull / current_commit / query_csv via
  asyncio.create_subprocess_exec — never blocks the shared event loop) + disk
  guard before pull.
- dolt_earnings_importer.py: detect_revision = pull + HEAD hash; stage = query
  earnings_calendar + eps_history, dedup, align, map act_symbol->ticker_id
  (normalize both sides so dotted BRK.B joins); promote is destructive
  (delete future dolt_earnings rows + upsert; past never deleted) so validate is
  FAIL-CLOSED — blocks when the staged forward calendar is empty or has collapsed
  below 50% of what's loaded (the forward calendar is the acceptance gate).
- NOTICE: CC BY-SA 4.0 attribution; config: DOLT_BINARY / DOLT_DATA_DIR / etc.

Verified end-to-end against the real 1.68 GB clone (5 tickers: 133 events, 128
paired, forward calendar to 2026-08-26, BRK.B joined). Tests: 9 alignment + 7
importer + 1 skip-guarded real-clone smoke. Full suite 699 passed.

Remaining for A2: wire the daily ~02:30 ET shadow cron — deferred to pair with
the deploy-time dolt install + DOLT_DATA_DIR provisioning.

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

NOTICE

@@ -0,0 +1,24 @@
+Third-party data attribution
+============================
+
+Earnings calendar and EPS history
+---------------------------------
+This application ingests the earnings calendar and EPS surprise history from the
+public DoltHub repository:
+
+    post-no-preference/earnings
+    https://www.dolthub.com/repositories/post-no-preference/earnings
+
+Licensed under Creative Commons Attribution-ShareAlike 4.0 International
+(CC BY-SA 4.0): https://creativecommons.org/licenses/by-sa/4.0/
+
+Use in this project: private, internal ingestion only. The data is normalized
+into PostgreSQL (`earnings_events`) — the announcement calendar is aligned to the
+EPS history via a minimum-cost monotonic pairing, symbols are normalized, and the
+session field is mapped to bmo/amc/unknown. No public API, bulk export, or
+redistribution of the data is provided. This attribution and the upstream license
+are preserved per the CC BY-SA 4.0 terms. Re-review licensing before any public
+or commercial access.
+
+The post-no-preference/stocks repository (workstream B) is not used at this time
+and would be reviewed separately.