feat: SyncQueue table and set-based apply stored procedure

- sql/01_sync_queue.sql: idempotent DDL for dbo.SyncQueue (PK + unique
  dedup index + pending lookup index), safe to re-run.
- sql/02_sync_apply.sql: dbo.usp_SyncApply (@MaxRetries INT=5). Per
  distinct (TargetSchema,TargetTable) it builds column projections from
  sys.columns (excludes ID key/computed/identity/rowversion) and runs a
  dynamic-SQL MERGE (last-write-wins via ROW_NUMBER over SourceLogID DESC)
  for Insert/Update plus a DELETE for the last op = Delete.
  SET IDENTITY_INSERT ON preserves Access PKs.
- tests/conftest.py: sql_conn fixture reads conn_str from gitignored
  config.yaml via load_config; skipped without RUN_INTEGRATION=1.
- tests/test_apply_proc.py: integration test covering IDENTITY-preserving
  INSERT, last-write-wins UPDATE, BIT conversion, and DELETE; cleans up.

Deviation from the brief's procedure (root-cause fix, design preserved):
every JSON path key is quoted ('$."col"') so non-ASCII column names
(e.g. Chinese 名字/数量) parse correctly. Without quoting, JSON_VALUE
raises "JSON path format is not correct" on Chinese columns, which is the
real target schema for this Access->SQL Server sync.

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

sql/01_sync_queue.sql

@@ -0,0 +1,42 @@
+-- SyncQueue: staging table for the Access -> SQL Server one-way sync.
+-- Idempotent: safe to re-run (table created only if absent; indexes only if absent).
+
+IF OBJECT_ID('dbo.SyncQueue', 'U') IS NULL
+BEGIN
+    CREATE TABLE dbo.SyncQueue (
+        QueueID      bigint IDENTITY(1,1) NOT NULL,
+        SourceFile   nvarchar(255)        NOT NULL,
+        SourceTable  nvarchar(255)        NOT NULL,
+        SourceLogID  bigint               NOT NULL,
+        TargetSchema nvarchar(128)        NOT NULL,
+        TargetTable  nvarchar(255)        NOT NULL,
+        RecordID     nvarchar(50)         NOT NULL,
+        OperateType  varchar(10)          NOT NULL,
+        RowData      nvarchar(max)        NULL,
+        Status       varchar(10)          NOT NULL CONSTRAINT DF_SyncQueue_Status  DEFAULT 'pending',
+        RetryCount   int                  NOT NULL CONSTRAINT DF_SyncQueue_Retry   DEFAULT 0,
+        ErrorMsg     nvarchar(max)        NULL,
+        CapturedAt   datetime2            NOT NULL CONSTRAINT DF_SyncQueue_Captured DEFAULT sysdatetime(),
+        AppliedAt    datetime2            NULL,
+        CONSTRAINT PK_SyncQueue PRIMARY KEY CLUSTERED (QueueID)
+    );
+END
+GO
+
+IF NOT EXISTS (SELECT 1 FROM sys.indexes
+               WHERE name = 'UX_SyncQueue_Dedup'
+                 AND object_id = OBJECT_ID('dbo.SyncQueue'))
+BEGIN
+    CREATE UNIQUE INDEX UX_SyncQueue_Dedup
+        ON dbo.SyncQueue(SourceFile, SourceTable, SourceLogID);
+END
+GO
+
+IF NOT EXISTS (SELECT 1 FROM sys.indexes
+               WHERE name = 'IX_SyncQueue_Pending'
+                 AND object_id = OBJECT_ID('dbo.SyncQueue'))
+BEGIN
+    CREATE INDEX IX_SyncQueue_Pending
+        ON dbo.SyncQueue(Status, TargetSchema, TargetTable);
+END
+GO