feat: access reader and value serialization

Add to_jsonable() (Access/pyodbc value -> JSON-safe) with strict TDD
(5 tests: datetime iso, bool preserved before int, decimal->str,
none/numbers, dict round-trip). bool branch precedes int because bool
is a subclass of int in Python.

Add AccessReader: reads TableChangeLog (read_log), reads a full source
row by RecordID via to_jsonable (read_row, warns on >4000-char values
that JSON_VALUE would truncate), and deletes processed log IDs in
chunked, retried batches (delete_log_ids, no-op on empty list).
Connects via the ACE ODBC driver from config.access.driver, shared
autocommit mode to coexist with the live .laccdb client.

Integration test against the real 氩弧焊.accdb (read-only; delete_log_ids
only exercised with []) passes.

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

tests/test_access_reader.py

@@ -0,0 +1,37 @@
+"""Integration test for AccessReader against the real 氩弧焊.accdb.
+
+READ-ONLY: this test never mutates production data. ``delete_log_ids`` is only
+exercised with an empty list (a guaranteed no-op) to confirm it does not raise.
+No real log rows are deleted.
+"""
+import os
+import pytest
+
+from sync.access_reader import AccessReader
+from sync.config import load_config
+
+
+@pytest.mark.integration
+def test_read_log_and_row_and_delete():
+    if not os.environ.get("RUN_INTEGRATION"):
+        pytest.skip("needs RUN_INTEGRATION=1")
+    cfg = load_config("config.yaml")
+    # Real live database (has a .laccdb lock from the client). Shared-mode
+    # read via ACE is validated to coexist with the lock.
+    db = os.environ.get(
+        "TEST_ACCDB",
+        r"\\192.168.110.114\生产进度表\2026年数据\氩弧焊.accdb",
+    )
+    r = AccessReader(db, cfg.access.driver)
+    try:
+        rows = r.read_log(500)
+        assert isinstance(rows, list)
+        if rows:
+            lr = rows[0]
+            assert lr.table_name and lr.record_id
+            assert lr.operate_type in ("Insert", "Update", "Delete")
+            d = r.read_row(lr.table_name, lr.record_id)
+            assert d is None or "ID" in d
+        r.delete_log_ids([], 100, 3)  # empty list -> no-op, must not raise
+    finally:
+        r.close()