refactor: introduce database provider abstraction, isolate MSSQL layer

- Add provider contract (src/providers/provider.js): query() -> {rows,
  rowsAffected, insertId}, callback transaction(fn), exec() for stored
  procs, initialize/purge lifecycle
- Add MssqlProvider (src/providers/mssql/index.js) wrapping an mssql
  ConnectionPool with normalized results, tx commit/rollback and
  constraint-error classifiers (unique 2627/2601, FK 547)
- LibDashStore constructor now takes a provider instead of a pool
  (breaking); adds LibDashStore.create() async factory; keeps pool as
  transitional bridge until store modules are converted (see TODO.md)
- Move MSSQL-specific code into the provider: src/sql/* ->
  src/providers/mssql/queries/*, src/schema.js ->
  src/providers/mssql/schema.js, purge SQL -> purgeSql.js
- Update scripts, generate-schema-graph.js and package.json exports
  (./providers/mssql, ./providers/provider)
- Add TODO.md with the remaining provider/SQLite migration plan

No SQL or behavioral changes.

src/store/delivery/attachments.js

@@ -1,5 +1,5 @@
 import { createHash } from 'node:crypto';
-import { LIST_BY_MANIFEST } from '../../sql/manifestattachment.js';
+import { LIST_BY_MANIFEST } from '../../providers/mssql/queries/manifestattachment.js';
 import request from '../request.js';
 import generateDocumentThumb from '../../util/generateDocumentThumb.js';
 import { parseMeta } from '../manifestattachment/listByManifestId.js';

src/store/delivery/create.js

@@ -4,7 +4,7 @@ import {
   CREATE_ATTACHMENT,
   GET_NEXT_ATTACHMENT_SORT,
   DELIVERY_TYPE,
-} from '../../sql/delivery.js';
+} from '../../providers/mssql/queries/delivery.js';
 import request from '../request.js';
 import resolveSelectedCompanyAccess from '../companyuser/resolveSelectedCompanyAccess.js';
 import nextNumber from '../numbers/nextNumber.js';

src/store/delivery/delete.js

@@ -1,4 +1,4 @@
-import { DELETE_MANIFEST, DELIVERY_TYPE } from '../../sql/delivery.js';
+import { DELETE_MANIFEST, DELIVERY_TYPE } from '../../providers/mssql/queries/delivery.js';
 import resolveSelectedCompanyAccess from '../companyuser/resolveSelectedCompanyAccess.js';
 
 export default function del(pool) {

src/store/delivery/helpers.js

@@ -2,7 +2,7 @@ import {
   DELIVERY_TYPE,
   GET_DELIVERY_HEADER,
   GET_DELIVERY_LINES,
-} from '../../sql/delivery.js';
+} from '../../providers/mssql/queries/delivery.js';
 import request from '../request.js';
 import { shapeLine } from '../manifestLines.js';
 import { loadAttachments } from './attachments.js';

src/store/delivery/list.js

@@ -1,4 +1,4 @@
-import { DELIVERY_TYPE, LIST_DELIVERIES, LIST_DELIVERY_FILES } from '../../sql/delivery.js';
+import { DELIVERY_TYPE, LIST_DELIVERIES, LIST_DELIVERY_FILES } from '../../providers/mssql/queries/delivery.js';
 import request from '../request.js';
 import resolveSelectedCompanyAccess from '../companyuser/resolveSelectedCompanyAccess.js';
 import { shapeSummary } from './helpers.js';

src/store/delivery/update.js

@@ -6,7 +6,7 @@ import {
   CREATE_FILE,
   CREATE_ATTACHMENT,
   UPDATE_MANIFEST,
-} from '../../sql/delivery.js';
+} from '../../providers/mssql/queries/delivery.js';
 import request from '../request.js';
 import resolveSelectedCompanyAccess from '../companyuser/resolveSelectedCompanyAccess.js';
 import taxEnsure from '../tax/ensure.js';

src/store/delivery/writeLines.js

@@ -1,4 +1,4 @@
-import { GET_SUPPLIER_BY_ID, SUPPLIER_GROUP_NAME } from '../../sql/entity.js';
+import { GET_SUPPLIER_BY_ID, SUPPLIER_GROUP_NAME } from '../../providers/mssql/queries/entity.js';
 import request from '../request.js';
 
 export async function assertSupplier(pool, tx, companyId, supplierId) {