Implement BAT-006: portfolio-hub ledger integration (REQ-017~019)

- REQ-017: LedgerPort contract (application/ledger_port.py) + portfolio-hub
  adapter + in-memory stub (adapters/ledger/), TREX_PORTFOLIO_HUB_* config
- REQ-018: fill→ledger recording in execution loop; FillStatus carries
  execution_id (deterministic synth) + fee; paper/kis adapters updated
- REQ-019: ledger outbox + retry worker (application/ledger_outbox.py),
  correlation_id idempotency, outcome vocabulary; 002_create_ledger_outbox.sql
- Tests: in-memory/portfolio-hub ledger, execution ledger hook, outbox,
  domain import sweep

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

trex_core/adapters/persistence/sql/002_create_ledger_outbox.sql

@@ -0,0 +1,33 @@
+-- BAT-006 / REQ-019: ledger outbox work-item store (dcy-004 OQ-2).
+--
+-- Each row is one fill that needs to be recorded in the portfolio-hub
+-- ledger. `correlation_id` ({asset_id}:{order_id}:{execution_id}) is the
+-- local dedup key — the same fill enqueued twice must NOT produce two
+-- ledger entries. Outcomes are classified per dcy-004 FR-4:
+--   completed | duplicate_completed | retryable_failure | conflict_blocked.
+
+CREATE TABLE IF NOT EXISTS ledger_outbox (
+    correlation_id   TEXT PRIMARY KEY,
+    asset_id         TEXT NOT NULL,
+    order_id         TEXT NOT NULL,
+    execution_id     TEXT NOT NULL,
+    side             TEXT NOT NULL CHECK (side IN ('buy','sell')),
+    qty              NUMERIC(18, 4) NOT NULL,
+    price            NUMERIC(18, 4) NOT NULL,
+    fee              NUMERIC(18, 4) NOT NULL DEFAULT 0,
+    tax              NUMERIC(18, 4) NOT NULL DEFAULT 0,
+    executed_at      TIMESTAMPTZ,
+    status           TEXT NOT NULL DEFAULT 'pending'
+        CHECK (status IN ('pending','completed','conflict_blocked')),
+    attempts         INTEGER NOT NULL DEFAULT 0,
+    last_outcome     TEXT
+        CHECK (last_outcome IS NULL OR last_outcome IN (
+            'completed','duplicate_completed','retryable_failure','conflict_blocked'
+        )),
+    last_error       TEXT,
+    created_at       TIMESTAMPTZ NOT NULL DEFAULT (now() AT TIME ZONE 'UTC'),
+    updated_at       TIMESTAMPTZ NOT NULL DEFAULT (now() AT TIME ZONE 'UTC')
+);
+
+CREATE INDEX IF NOT EXISTS idx_ledger_outbox_status_created
+    ON ledger_outbox (status, created_at);