inbound-antispam-panel: migration 0002, journal and filter-list tables

Step 2/12 of docs/plans/inbound-antispam-panel.md, the first migration
after the 2.0 baseline (2.0.1 was cut before it, as agreed).

0002_inbound_spam_log.sql adds inbound_spam_log (one row per recipient:
domain, client IP, envelope, subject, decision, engine, detail) with
indexes on created_at and (inbound_domain, created_at), and
inbound_spam_list (allow / deny entries, unique per list). DDL only;
decision, engine, list_type and entry_type carry CHECKs, as the
baseline does for its own enumerations. Nothing reads or writes the
tables yet.

Tests: TestBaselineSchema pins both tables and user_version 2;
TestOpenMigratesA20Database opens a file holding the baseline alone and
finds its user kept; TestInboundSpamConstraints.

go test ./internal/store/ ok; go vet ./... ok.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -5,6 +5,13 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
 
 ## [Unreleased]
 
+### Added
+
+- Schema: migration `0002_inbound_spam_log.sql`, the first after the 2.0
+  baseline - two empty tables for the inbound antispam journal and the filter
+  lists (inbound-antispam-panel). A 2.0.x database is migrated when the panel
+  starts; nothing reads or writes the tables yet.
+
 ## [2.0.1] - 2026-10-11
 
 ### Changed